MDI and TDI: Safety, Health and the Environment. · 2 Handling MDI and TDI Pride in safety Safety is a critically important aspect of all activities involved in the handling of chemicals

MDI and TDI: Safety, Healthand the Environment.A Source Book and Practical Guide

Edited by:

D C AllportGilbert International Ltd, Manchester, UK

D S GilbertGilbert International Ltd, Manchester, UK

and

S M OuttersideGilbert International Ltd, Manchester, UK

Copyright 2003 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester,West Sussex PO19 8SQ, England

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Library of Congress Cataloging-in-Publication Data

MDI and TDI : safety, health and the environment. A source book and practical guide / edited byD.C. Allport, D.S. Gilbert, and S.M. Outterside.

p. cm.Includes bibliographical references and index.ISBN 0-471-95812-3 (alk. paper)1. Isocyanates – Safety measures. 2. Methylenediphenyl diisocyanate – Safety measures. 3.

Toluene diisocyanate – Safety measures. I. Allport, Dennis C. II. Gilbert, D. S. III.Outterside, S. M.

TP248.I8 M45 2002668.4′239′0289–dc21 2002033117

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0-471-95812-3

Typeset in 10.5/12.5pt Times by Laserwords Private Limited, Chennai, IndiaPrinted and bound in Italy by Conti TipcolorThis book is printed on acid-free paper responsibly manufactured from sustainable forestry in whichat least two trees are planted for each one used for paper production.

While the International Isocyanate Institute (“III”) has supported the preparation of this text,the views expressed therein are those of the authors and not necessarily those of the III or itsmembers. While great care has been taken in the preparation and editing of this text, neitherthe III, its members, nor the authors or editors of this text can accept responsibility for anyerrors or omissions therein. While the text discusses certain of the manufacturing, handling,environmental, medical and other aspects of the diisocyanate industry, it does not purport tobe, and is not, a comprehensive guide thereto.

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Contents

List of authors and affiliations ixA book of distinction xvAcknowledgements xvii

Part PageMDI and TDI usage: responsible riskmanagement 1D C Allport, D S Gilbert andS M Outterside

Exposure, hazard and risk 1Responsible Care: a frameworkfor industry action 5Reading 10

1 MDI, TDI and the polyurethaneindustry 11D C Allport, D S Gilbert andS M Outterside

Types of MDI 13Types of TDI 15Test substances 16Misapprehensions 16Polyurethanes made from MDI andTDI 17Reading 23

2 Handling MDI and TDI 25D C Allport, R C Blake, C Bastian,C Galavitz, D S Gilbert, R Hurd,B Reeve, W Robert, S M Outterside,A Solinas, D Walsh, U Walber andH Wolfson

Pride in safety 25Successful systems 25Safety systems for thehandling of MDI and TDI 26

Part PageKey Theme 1: Know your product

Health 31Environment 32

Key Theme 2: Protecting health 33Duty of care 33Exposure: how can MDI orTDI enter the body? 34Medical symptoms 35Medical checks 36

Key Theme 3: Neutralization,decontamination and disposal ofwastes

Types of neutralizer 40Routine cleaning ofequipment and drums 40Neutralization after a spillage 43Neutralizer formulations 46

Key Theme 4: Using personalprotective equipment 47

Normal operations 47Emergency situations 48Selection of personalprotective equipment 49Protective clothing 50Respiratory protection 51

Key Theme 5: Monitoring exposure 59How should monitoring becarried out? 60When should monitoring becarried out? 61

Key Theme 6: Dealing withaccidents 62

Accidents can happen 62Spillages 63Development of excesspressure inside containers 68Incidents involving fire 70

2

39

9

vi Contents

Part PageTransport of MDI and TDI 72

Transport regulations 73MDI and TDI: transporttemperaturesTypical containers for thetransport of diisocyanates 75Accidents and emergencies 85

The workplace: storage and use ofMDI and TDI 86

Designing the systems andminimizing the risks 87Physical and chemicalproperties relating to storageand processing 93Storage of MDI and TDI 95Safety issues in workplacesusing MDI and TDI 106Safety issues in someimportant polyurethaneprocesses 117Use of MDI and TDI inlaboratories 122Visitors to the workplace 123Emergencies in the workplace 124

Releases to atmosphere frompolyurethane manufacturing sites 126

Properties of MDI and TDIrelevant to releasesto atmosphere 127Releases from polyurethaneprocessesAbatement of releases

Reading

3 Health 155D C Allport, P Davies, W F Diller,J E Doe, F Floc’h, H D Hoffmann,M Katoh and J P Lyon. Appendices byD I Bernstein

Perspective on immediate effectsfollowing over-exposure 156First aid procedures 156

Commentary on first aidprocedures 157

Human health: the medicalbackground 160

Effects on the eyes 163Effects on the skin 163

Part PageEffects when swallowed 165Effects on the respiratory tract 165Other health effects of MDIand TDI 185Biomonitoring of MDIand TDI 186

Experimental toxicology 187The interaction of MDI andTDI with biological systems 188Toxicology studies 193

Diagnosis of diisocyanateasthma 203Appendices (David I. Bernstein) 203Reading 217

4 The environment 229R E Bailey, A Gard, K H den Haan,F Heimbach, D Pemberton, H Tadokoro,M Takatsuki and Y Yakabe

A general approach toenvironmental risk assessment 229Exposure 233

Sources of exposure 233Distribution andpersistence 237Biodegradation 256Bioaccumulation 257

Hazard 258Test procedures 258Aquatic ecotoxicity 259Terrestrial ecotoxicity 264

Risk assessment 265Accidental release of MDIand TDI 266Normal usage 268

Reading 2735 Supporting sciences 277

5.1 Chemistry of manufacture of MDIand TDI 277D C Allport, D S Gilbert andB Tury

Manufacture of MDI 277Manufacture of TDI 280Modified MDI and TDI 282

Reading 2845.2 Structures and nomenclature 285

D C Allport, D S Gilbert andB Tury

7

148

4

12138

8

Contents vii

Part PageStructures 285CAS Registry numbers andpreferred names 286IUPAC names 287Convenient names for MDIand TDI 288Synonyms 289Commercial product names 289Reading 291

5.3 Chemical reactions of MDIand TDI 291D C Allport, D S Gilbert,D Pemberton and B Tury

Reaction with –OH groups 292Reaction with –NH groups 293Reaction with –SH groups 293Reaction with biologicalmolecules 294Self-reactions 295Catalysts 298

Reading 2995.4 Physical and fire properties 300

S M Outterside and D PembertonMDI 301TDI 311

Reading 3205.5 Fire behaviour of MDI and TDI 321

J F Chapman, B Cope, G Marlairand F Prager

Part PageTest methodology 321Fire tests on MDI and TDI 323

Reading 3405.6 Occupational exposure limits, stack

limits and community limits 343D C Allport, D S Gilbert,S M Outterside and B Tury

Occupational exposure limits 343Stack release limits andcommunity limits 351

Reading 3585.7 Sampling and analysis 358

K S Brenner, V Dharmarajan andP Maddison

Materials to be measured 358Airborne MDI and TDIspecies 359Choice of methods for thesampling and analysis of MDIand TDI in air 361Analysis of nonairborne MDIand TDI 418A critical review of exposureassessment techniques used inoccupational health studies ofMDI and TDI 421

Reading 423

Index 431

2 Handling MDI and TDI

Pride in safety

Safety is a critically important aspect of all activities involved in the handling ofchemicals. The protection of the health of those who may possibly be exposedto MDI and TDI and the preservation of the environment can never be seen asoptional. Safety does not, of course, simply ‘happen’. Safe working practicescan be achieved only by the active management of all relevant tasks. A safetysystem must start at the top of the organization. Managers should wish to ensurethat there is careful and responsible management of all safety-related activities,that adequate material and human resources are provided, and that safety is seento be a business priority. The design and implementation of a safety systemthat is practical, that uses resources effectively, and that is understood andactively implemented by the entire workforce should call upon a wide diversityof knowledge and skills in any enterprise. A considerable body of technicalknowledge will need to be available, and effective ongoing communicationwith many individuals inside and outside the group will be necessary. Theownership of safety and environmental protection is the responsibility of theentire workforce and there needs to be a clear understanding by all staff oftheir particular responsibility in the overall safety system. A successful safetysystem will therefore rightly be a source of considerable pride and satisfactionthroughout any organization since it involves staff at all levels and the resultswill be plainly visible to all. The principles outlined below are equally relevantto any size of organization.

Successful systems

Successful systems that meet internal and external needs in an ongoing mannershare several characteristics (Figure 2.1):

• they are owned and managed;• they are recorded and communicated;• they are assessed regularly and are subject to corrective action and improve-

ment.

Owned and managedA system has no life of its own. It cannot simply appear when it is needed, andit cannot revise itself to take account of new understanding and experience,

26 MDI and TDI: Safety, Health and the Environment. A Source Book and Practical Guide

Continualimprovement

Planning andwriting

procedures

Assessing andcorrective

action

Managementreview

Implementationand operation

Safetypolicy

Figure 2.1 Characteristics of a successful safety system

or of changed circumstances. These matters must be the responsibility of anassigned manager of the safety system.

RecordedAll users of a system need to know how it works and what exactly they have todo. They must be involved in the compiling of the system, since safe workingpractices must take account of the practicalities of carrying out daily work.Clear and brief written procedures are a valuable source of communicationand training material for new staff and will also be useful in refresher training.Written procedures will help to ensure they are not simply passed on verbally,possibly giving rise to poor work practices.

Assessed and improvedAll systems can be improved, especially in the light of experience. Even thebest systems can go wrong! The only way to ensure that everyone knowswhat is expected and that the agreed procedures are actually followed is byregular assessment or inspection. Any deficiencies in adhering to the systemand any problems arising from the system itself will be the subject of correctiveactions and, where necessary, of improved procedures. Improvement is therebyencouraged and is built into the system.

Safety systems for the handling of MDI and TDI

A safety system will need to pay attention to several key areas:

• organizational matters, including the clear allocation of responsibilities,requirements for measurement, reporting and communication, and mech-anisms for review and improvement of the safety system;

• operational procedures for safe working, including those relevant to thehandling of materials and to the operation and maintenance of equipment;

Handling MDI and TDI 27

• personnel matters including training, and medical surveillance;• planning for emergencies.

Each organization will develop its own list of critical safety procedures that arerelevant to its own circumstances. All the general questions arising from ISO9001, Model for quality assurance in design, development, production, instal-lation and servicing are important and should be addressed in a comprehensivesafety system. The further questions may need to be modified according to theparticular polyurethane operation under consideration, and other questions willalmost certainly arise in most operations.

General questions:

• Does the safety system cover all aspects of transportation, storage and use?• Does everyone know what he or she is responsible for, and is this checked

periodically?• Are all critical procedures and instructions written down, and are current

versions provided to those who have to implement them?• Does the system meet all supplier, customer and regulatory requirements?• Are all materials used in the production processes supported by adequate

documentation, identification and stock control?• Are there adequate inspection and test procedures to ensure safe working

practices?• Are substandard materials rigorously identified, labelled and segregated in

such a way that they cannot be used accidentally?• Are corrective actions put in place to correct deficiencies in the operation

of the system, and to find solutions to any problems with the system itself?• Are records available to demonstrate that all critical procedures are complied

with, and is there a regular review of these records?• Is adequate training and refresher training provided to ensure that all safety

procedures are understood and can be properly implemented?

Further questions that may be relevant to the handling of diisocyanates:

• Is the latest safety information, especially that from suppliers, available onthe diisocyanates and equipment that are being used?

• Is the MDI or TDI held at the correct temperature?• Have adequate steps been taken to prevent contamination, especially by

water?• Are the safest methods used to transfer materials to the storage facilities?• How is it known that safety equipment, including alarms, is available, is

effective and is fully functional at all times?• Does the system prevent unacceptable releases of diisocyanates to the work-

place or the environment?• Is the ventilation system able to cope with likely changes in conditions

caused, for example, by fans, open doors and windows?• Are changes in manufacturing processes accompanied by workplace moni-

toring (industrial hygiene sampling)?• Is there regular diisocyanate medical surveillance for the potentially exposed

workforce?• Are adequate emergency procedures in place and tested?


Many organizations have decided to develop their safety systems further to theextent of having them submitted for regular internal audit, or for registrationunder national or international quality assurance standards with regular externalaudit. By these means, companies ensure that their safety and environmentalprotection systems are maintained to a high standard, thus providing evidenceof their competence.

Two important International Standards for systems that are appropriate forsafety and environmental protection are

ISO 9001:1994 Model for quality assurance in design/development,production, installation and servicing. There arerelated national standards.

ISO 14001:1996(E) Environmental management systems – specificationwith guidance for use.

Check lists, which cover many important aspects of safety, are available.

• Bulk storage facilities and equipment (SPI, 1996a, 1996b)• Inspection of transport equipment (ISOPA, 1992)• Unloading rail tank cars (SPI, 1996c, 1996d)• Unloading tank trucks/ road tankers (SPI, 1996e, 1996f; ISOPA, 1992)

Diisocyanate suppliers and trade associations should be approached for fur-ther lists.

Information for the safety system

The working procedures that are part of the safety system will need to takeaccount of the best practices elsewhere and of local conditions, so that effec-tive solutions can be provided. It is clearly useless, for example, to write downprocedures that are going to be disregarded because of the lack of equipment,because of lack of understanding, or because their implementation would inter-fere with other required work activities. This part of the book is concernedparticularly with work practices that have been found to be satisfactory invery many companies, and which form the foundation for many safety proce-dures. Detailed work practices are examined that are relevant to safety in thetransportation, storage and the handling of MDI and TDI in the workplace.Several Key Themes have been identified that are relevant to many operations,and which will provide useful information in the design of safety systems.These are:

Key Theme 1: Know your productKey Theme 2: Protecting healthKey Theme 3: Neutralization, decontamination and disposal of wastesKey Theme 4: Using personal protective equipmentKey Theme 5: Monitoring exposureKey Theme 6: Dealing with accidents

Each Key Theme has been written to be used as an independent text and thereis, therefore, some repetition of basic concepts and information.


Key Theme 1: Know your product

In order to handle chemicals safely, it is necessary to know their toxicological,chemical, physical and fire properties. This Key Theme provides the informa-tion on the basic properties which is needed for the safe handling of polymericMDI, pure MDI and TDI. The properties of MDI or TDI as related to handlingare almost the same, irrespective of supplier. However, there is a very widediversity of other MDI- and TDI-based products, including chemically modifieddiisocyanates and solvent grades, and these have their own specific properties.In order to be able to handle these proprietary products safely it will be nec-essary to consult documentation from the supplier, notably the material safetydata sheets. The headings often included in material safety data sheets are listed

In this text, the term Materialsafety data sheet (MSDS) isused. In the European Unionthe term Safety data sheetmay be used.

below, along with the relevant parts of this book in which there is detailedinformation on those topics, as related to polymeric MDI, pure MDI and TDI.

Topics covered by manufacturers’ material safety data sheetsTopic Source

Hazards of the substanceor preparation

Part 2, Handling MDI and TDI: Key Theme2, Protecting health

Part 3, HealthPart 4, The environmentPart 5.5, Fire behaviour of MDI and TDI

First aid measures Part 2, Handling MDI and TDI: KeyTheme 6, Dealing with accidents

Part 3, Health

Fire-fighting measures Part 2, Handling MDI and TDI: KeyTheme 6, Dealing with accidents

Accidental releasemeasures

Part 2, Handling MDI and TDI: KeyTheme 6, Dealing with accidents

Part 2, Handling MDI and TDI: KeyTheme 3, Neutralization,decontamination and disposalof wastes

Handling and storage Part 2, Handling MDI and TDI:The workplace: storage and useof MDI and TDI

Exposure controls andpersonal protection

Part 2, Handling MDI and TDI:The workplace: storage and useof MDI and TDI

Part 2, Handling MDI and TDI: KeyTheme 4, Using personal protectiveequipment

Physical and chemicalproperties

Part 5, Supporting sciences: Parts 5.3and 5.4

Stability and reactivity Part 5.3, Chemical reactions of MDI and TDIPart 4, The environment


Toxicology Part 3, Health

Ecotoxicology Part 4, The environment

Disposal Part 2, Handling MDI and TDI: KeyTheme 3, Neutralization,decontamination and disposalof wastes

Part 2, Handling MDI and TDI:The workplace: storage and useof MDI and TDI

Transport Part 2, Handling MDI and TDI: Transportof MDI and TDI

Regulatory exposurerequirements

Part 5.6, Occupational exposure limits, stacklimits and community limits

Some useful properties of the commonly used MDI and TDI products aregiven in Table 2.1. More extensive data will be found in Part 5.3, Chemicalreactions of MDI and TDI and Part 5.4, Physical and fire properties.

Table 2.1 Basic information on MDI and TDI.

Polymeric MDI Pure MDI 80/20 TDI

Appearance Brown liquid White solid Colourless to paleyellow liquid

Relative density at 20 ◦C(to that of water at 4 ◦C)

1.24 1.33 1.22

Melting point ◦C (◦F) 5 (41) 40 (104) 10 (50)Viscosity at 20 ◦C Slightly viscous liquid Solid Mobile liquid

cP (=mPa s) 300 3(product dependent)

Reaction with water Interact slowly with release of carbon dioxide gasFire properties Not easily ignitable and not explosive

At factory temperatures, both polymeric MDI and 80/20 TDI are liquids,whilst pure MDI is a solid. All are significantly denser than water (Table 2.1)and will therefore sink when in water or aqueous mixtures. Both polymericMDI and TDI can solidify at low temperatures which may be encountered dur-ing transport and storage. The temperatures at which they are to be processedwill often determine suitable storage temperatures for polymeric MDI and TDI.It is usually best to maintain them at 15 to 25 ◦C (59 to 77 ◦F): this gives asuitable balance of viscosity and product storage life. Pure MDI melts at about40 ◦C (104 ◦F) and must be either stored frozen below 5 ◦C (41 ◦F), or held inthe liquid state between 40 and 45 ◦C (104 and 113 ◦F). More information isgiven in Part 2, The workplace: storage and use of MDI and TDI.

MDI and TDI are reactive chemicals. The diisocyanates react with a range ofcommon chemicals, in many cases vigorously with the evolution of heat. Allcontamination of MDI and TDI must be rigorously avoided. Contaminationwith water, including moisture from the air, will lead to the generation of


carbon dioxide. This will result in the development of excess pressure in closedcontainers. This pressure build-up can be sufficient to rupture a sealed drumwith great violence. Alkalis such as sodium hydroxide or potassium hydroxidecan react violently with diisocyanates.

Both MDI and TDI are very much less volatile than water. TDI has a sat-urated vapour concentration about one thousandth of that of water. At roomtemperature MDI is even less volatile, with a saturated vapour concentrationof about one ten millionth of that of water. However, even very low concen-trations of MDI or TDI can cause respiratory problems whether as vapour oras aerosols.

Usual state of MDI and TDI in air

MDI Vapour and/or aerosolTDI VapourSpray applications

with MDI or TDIAerosol

Health

Over-exposure to MDI or TDI can lead to adverse respiratory effects, whichmay include the development of asthma (Table 2.2). Strict observance of thepermitted occupational exposure limits is therefore necessary. Once asthmahas developed, and a person has become sensitized to a diisocyanate, evenconcentrations well below the permitted exposure levels can be sufficient toinduce an asthmatic attack. Vapours, aerosols or splashes of MDI or TDI maycause irritation to the eyes. MDI and TDI are moderate skin irritants, and maycause skin sensitization or dermatitis in rare cases. Both MDI and TDI havelow toxicities when swallowed. If any health problems occur that are thoughtto be associated with over-exposure to the diisocyanates, then medical attentionshould be sought immediately.

Table 2.2 Health effects of MDI and TDI.

Pure MDI Polymeric MDI 80/20 TDI

Odour Cannot be detected by smell unless concentrations are wellabove the occupational exposure limits

Respiratory effects May cause respiratory irritation and asthmaEye irritation May be irritant to the eyesSkin irritation May cause moderate skin irritationOral toxicity Have very low toxicities when swallowed

Long-term studies on the health of workers exposed to MDI or TDI haveshown no exposure-related clinical effects other than the development of respi-ratory symptoms. Animal studies, which give further background information,are discussed in Part 3, Health of this book.


Occupational exposure limits are indicators of airborne concentrations ofsubstances to which nearly all workers may be repeatedly exposed day after daywithout adverse health effects. They are usually mandatory for many chemicals.There is good agreement globally on the limits that should apply to short-term

See Part 5.6, Occupationalexposure limits, stack limitsand community limits formore detailed information.

exposure (for example, 15 min) or long-term (8 h) exposure. The limits forairborne MDI or TDI may be expressed in parts per billion (volume in volumeof air) or in concentration (weight in volume of air). Table 2.3 gives the limitvalues commonly adopted for airborne diisocyanates.

Table 2.3 Occupational exposure limits: typical values.

Short-term (15 min) Long-term (8 h)

mg/m3 ppb mg/m3 ppb

MDI 0.2 20 0.05 5TDI 0.14 20 0.036 5

It can be seen that the limits for MDI and TDI are the same when they areexpressed in parts per billion, and very similar when expressed as milligramsper cubic metre. At 20 ◦C (68 ◦F) MDI will not volatilize enough to achieve theshort-term occupational exposure limit, whereas TDI will significantly exceedthe limit, as shown in Figure 2.2. At 30 ◦C (86 ◦F) saturated vapour concen-trations of MDI and TDI both exceed the occupational exposure limits.

40,000

10,000

252015105

15 20 25 30

20,000

30,000

TDI

MDI

OEL−TWA

OEL−ceiling

PMDI

Con

cent

ratio

n (p

pb)

Temperature (°C)

Figure 2.2 Vapour pressure-temperature curves for MDI and TDI

Environment

Releases of MDI or TDI into the environment are not persistent, being degradedin air and in water. The diisocyanates are so inherently reactive in water as to be

See Part 4, Theenvironment.


virtually unavailable for biological uptake or bioaccumulation, and the majorproducts are inert, insoluble polyureas. As a result, environmental exposure toMDI or TDI, arising either from normal use or accidental release, is very low.Both MDI and TDI show generally low toxicity to a wide range of water- andsoil-based organisms: bacteria, algae, fish, invertebrates and plants.

Key Theme 2: Protecting health

First aid guidelines are given in Part 3, Health.

Duty of care

All possible routes of exposure should be avoided. Avoidance of inhalation ofMDI or TDI as vapour, aerosols or dusts is of particular importance becauseof possible respiratory problems.

The transport, storage and use of MDI and TDI should not therefore beundertaken without a proper understanding of the potential health risks in-volved. There need to be effective systems for the protection of the healthof personnel in the workplace. At all times the guiding principle must be toensure that releases of all types are below those levels at which adverse effectsmay occur. Good workplace procedures are essential. Engineering design ofpolyurethane manufacturing equipment and controls should be used wheneverpossible to reduce exposure to diisocyanates. Adequate ventilation is usu-ally necessary to prevent worker exposure for many processing operationsinvolving MDI or TDI. Planning must nevertheless also take into accounthow to respond to those situations where excessive short-term releases occurbecause of an accident. The implications of normal or accidental releases onthe nearby community also need to be considered. Experience over the past 30to 40 years has shown that the application of these principles of minimizinghuman exposure has led to a continuous reduction in adverse health effects.Companies should be encouraged to develop their safety-at-work systems asan on-going activity.

The occupational exposure limits in force must always be observed. Theprocedures necessary will normally include a programme of workplace moni-toring and documentation to ensure compliance. It is necessary to measure theconcentrations of diisocyanates in the atmosphere to find out if any situationsrequire corrective action. Some direct reading analytical instruments are avail-able for this purpose (see Part 5.7, Sampling and analysis). It is imperative thatbuilt-in safeguards such as alarms are used to alert workers to over-exposures.There should be good evidence to show that these safeguards are fully effectiveat all times.

Over-exposure to MDI or TDI may cause irritation of the nose and lungs,feelings of tightness in the chest and difficulty in breathing; repeated over-exposure may lead to asthma-like attacks. MDI and TDI may also causeirritation of the eyes and skin.

Training in first aid specific to the handling of MDI and TDI should beprovided for staff in all workplaces where diisocyanates are handled. It should


be standard practice to ensure that all staff working in areas where diiso-cyanates are transported, stored or used have a full understanding of thepotential health effects and of the safe working practices recommended fortheir site. These should include first aid and decontamination procedures tobe followed in the event of a spill or leak. First aid treatment is discussed indetail in Part 3, Health.

Exposure: how can MDI or TDI enter the body?It is obvious that there can be no health impact if substances are preventedfrom entering the body in the first place. The entry points for chemicals intothe body are:

• into the respiratory system (Figure 2.3) by the inhalation of a vapour, aerosolor dust;

• through the skin, especially if damaged by cuts or open wounds;• by contact with the eye;• through the mouth by swallowing, or by eating contaminated food or drink;• by smoking.

Trachea

Alveolus

Alveolarduct

Alveolar sac

Larynx

Pharynx

Bronchiole

Right mainbronchus

The respiratory system islike an inverted tree in thechest cavity. The tree hashollow branches. The trunkis the windpipe (trachea),which splits into thebronchial tubes. As thebronchial tubes divide, theybecome thinner and thinneruntil they becomebronchioles. Bronchiolesare about the diameter of acotton thread. Each oneterminates in a tiny sac(alveolus) where gasexchange occurs.

Figure 2.3 The human respiratory system

MDI and TDI react readily with biological substances, and will thus not cir-culate around the body in their original forms.


Possible types of exposureAs vapourIf workplace air containing MDI or TDI is inhaled, some of the diisocyanatecan be carried into the lungs after passing the throat and upper respiratorytract. At ambient temperature, the vapour concentration of TDI may exceedthe long-term occupational exposure limit. The vapour concentration of MDIcan reach the occupational exposure limit at elevated temperatures. At theextremely low concentrations usually found in the workplace, MDI and TDIas vapours are carried along with the air with which they mix. There is noseparation or layering.

As aerosolIn certain situations very small droplets or particles (aerosols), of MDI inparticular, may be produced. In contrast to gases, which contain individualmolecules of diisocyanate, aerosols are particles of liquid or of solid, containingmany molecules. Whilst it is sometimes possible to see mists of larger droplets,many aerosols are quite invisible to the naked eye even under favourablelighting conditions. These smaller particles are of special concern becausethey have the potential to be inhaled and carried into the lungs. Only thoseparticles of less than about 10 to 15 µm are respirable; larger particles aredeposited in nasal passages and the upper respiratory tract. Larger aerosolparticles may be deposited on working surfaces, where they could give riseto skin contamination. Spraying operations are the main source of aerosols.

See Part 3, Health for moredetails on exposureto aerosols.

Aerosols are also produced when a vapour at elevated temperatures coolsto below its saturated vapour concentration. Aerosols of reacting mixtures ofpolyurethane components may be present in spraying operations. In these casesthe concentration of diisocyanate decreases rapidly as the reaction proceeds.

As dustsDusts of pure MDI may be encountered when flaked, solid material is handled,or if solid residues are cleaned up by scraping or brushing. It is also possiblefor particles of dust from other workplace materials such as wood to havediisocyanates adsorbed in certain circumstances. Particles of less than about10 to 15 µm are respirable.

As liquidsExposure may occur by contact of the skin or the eyes with polymeric MDIor TDI or with any form of MDI or TDI dissolved in solvents.

Medical symptoms

There are usually no health effects resulting from exposure to MDI or TDIbelow the occupational exposure limits. However, a brief, single high exposure

See Part 3, Health fordetailed information.

to diisocyanates may trigger an airway response, even if the average concen-tration for a period of 15 min is below the permitted occupational exposurelimits. The topic is covered in more detail in Part 3, Health and occupationalexposure limits are discussed in Part 5.6, Occupational exposure limits, stack


limits and community limits. The onset of the clinical signs of irritation, suchas watering eyes, sore throat, or cough, occurs at much higher levels than thepermitted occupational exposure limits.

At the maximum allowable workplace exposure levels MDI and TDIcannot be detected by the human sense of smell. Odour should never berelied upon as an indication of exposure to MDI or TDI. If a worker cansmell them, over-exposure is occurring.

Odour thresholds

Odour thresholds for TDI and MDI have been determined by exposingpanels of volunteers to different levels of the test substance. In onestudy (MCA, 1968) recognition of the odour of TDI was achieved by50 % of the panel at 200 ppb TDI, but over 2000 ppb was needed for100 % recognition. In another study (Henschler et al., 1962), 50 ppbwas sufficient for over 90 % recognition. The odour of polymeric MDIwas detectable at 400 ppb according to one report (Woolrich, 1982).Too much emphasis should not be placed on these values as:

• the values may not be accurate due to some of the analytical andsampling methods used.

• obtaining stable concentrations of diisocyanate vapours and aerosolsin a test room is very difficult due to their adsorption onto surfaces.

• human odour perception is very unreliable and fatigues easily atthreshold levels.

From inhalationThe main risk from diisocyanatesarises from inha-lation of vapours,aerosols or dusts. MDI and TDIwill act primarily as respiratoryirritants. In mild cases the affectedperson may experience slight irritationof the nose and throat, possiblycombined with dryness of the throat.In severe cases the person may sufferacute bronchial irritation and difficultyin breathing. Individuals who havedeveloped sensitivity to MDI or TDImay develop asthma and experiencewheezing, tightness of the chest andshortness of breath. Symptoms of both

irritation and sensitization may be delayed for several hours after exposure.Coughing at night may be a symptom of sensitization. A hyperreactive responseto even minimal concentrations of MDI or TDI may develop in sensitizedpersons or in persons with hyperreactive airways.

From skin contactMDI and TDI are moderate skin irritants. In rare cases, repeated or prolongedcontact may cause skin sensitization. There are differing views of researcherson the possible contribution of skin contact of MDI and TDI to the developmentof respiratory disease.

From eye contactTDI in the form of an aerosol, liquid or vapour may cause eye irritation. In veryrare instances, severe eye contamination may cause lasting damage (cornealscars). Overall, MDI appears to be somewhat less irritating.

Medical checks

Minimization of exposure is the prime defence against health problems andshould be supported by engineering controls, by regular monitoring of work-place exposure where appropriate, by the use of relevant protective clothingand by proper education of the work force. These measures should be sup-ported by active medical surveillance of the workforce. Various systems are in


operation in different countries, in part to meet particular national requirementssuch as those for compensation schemes. National requirements must alwaysbe followed in setting up a medical surveillance scheme for diisocyanate work-ers. Medical surveillance concentrates on the respiratory tract, in which mostproblems occur in practice. This surveillance usually involves measuring lungfunction and compiling a detailed respiratory history.

The most commonly used way of determining lung function in humansinvolves measuring the rate and extent to which the lungs can move air in andout of the respiratory system by constructing a flow–time curve depicting airmovement over time (Figure 2.4). Testing is typically conducted under con-ditions requiring maximal effort by the person being evaluated. Flow-volumedata may be produced in graphical or digital format depending on the type ofmeasuring device (spirometer) selected. Standard prediction equations or refer-ence tables have been developed for different groups of people to improve theclinical interpretation of spirometric results, because the ventilatory capacity ofthe lungs is known to decline gradually with increasing age, even in the healthi-est of individuals. Data from flow-volume measurements may depend on manyother variables, including stature, gender, race, nutritional state, health, smok-ing history, weight and physical fitness. The interpretation of lung functiondata is a specialised task.

00 1 2 3 4

1

2

3

FEV1

FVC

4

Time (seconds)

Vol

ume

exha

led

(litr

es)

FEV1 and FVC are measured witha spirometer, an instrument thatmeasures the volume of exhaledbreath versus time.

FVC: The forced vital capacity is the total volume of air that can be exhaled using maximumeffort, following a full breath.

FEV1: The forced expiratory volume is the volume of air that can be exhaled in one second usingmaximum effort, following a full breath.

Spirometry volume–time curve

Figure 2.4 Spirometry


It is normal good industry practice for lung functions to be measured:

• prior to employment in work with MDI or TDI;• during routine monitoring of health;• on return to work after certain illnesses;• if respiratory problems are suspected by medical staff;• as part of the diagnosis of asthma;• as part of a final examination on leaving employment using diisocyanates;• after incidents or emergencies involving diisocyanates.

The most common parameters derived from the volume–time curves are theforced expiratory volume in one second (FEV1) and the forced vital capacity(FVC). Accurate measurement of these parameters requires the active cooper-ation and maximum effort of the individual being tested. Standards have beendeveloped to assure the consistency and accuracy of results. For example, atleast three tests are generally performed so that reproducibility may be judged.In part because of their simplicity, FEV1 and FVC have remained the mostwidely used measures for describing lung function performance.

Regulatory bodies and other organizations may issue recommendations formedical surveillance of diisocyanate workers. Such recommendations may

Health surveillancerecommendationsHVBG (1998); HSE (1997a,1998); BRMA and Rapra(2001); NZ OSH (1998).

include:

• a pre-placement examination;• routine periodic examinations;• re-examination on return to work following a sickness absence.

Timing of examinations

• Pre-employment: a pre-placement examination will provide a baseline foreach employee against which any subsequent examination can be comparedto detect changes, and to identify subjects at increased risk due to existingrespiratory disease. Testing will also check whether workers have the abilityto use respirators, if needed. A pre-employment examination is obviously notpossible where a health-surveillance scheme is introduced into an existingworkforce, and an initial examination at the time of introduction must beperformed as a baseline.

• During employment: examinations at 2 and 6 weeks after the start of diiso-cyanate work are also recommended in workplaces with measurable levels ofdiisocyanates, to identify those people who may become sensitized rapidly,or who react adversely even to very low atmospheric diisocyanate concen-trations because of pre-existing nonspecific bronchial hyperresponsiveness.Thereafter, it is of value to carry out routine examinations at intervals. Theinterval may range from 3 months to 2 years, depending on the prior medicalhistory and the expected exposure levels of an individual.

• After absence for sickness: if a diisocyanate worker has had significantabsence due to respiratory disease, the examination should be repeated. Sig-nificant sickness absence is considered to be more than 2 weeks, or repeatedshorter absences.


• Final examination: it is desirable to have a final examination at the time offinishing diisocyanate work. This is useful in order to assess whether anysubsequent illness is related to diisocyanate exposure.

Content of examinationsThe following is recommended as a minimum:

• History: interview with a structured questionnaire. An example of a suitablequestionnaire is provided in Part 3, Health. This should cover the generalmedical and occupational history with special attention being paid to chronicand allergic chest diseases, and to smoking.

• Clinical examination with emphasis on the respiratory system.• Pulmonary function tests: normally forced expiratory volume in one second

and forced vital capacity.

Spirometry: further considerations

A correctly calibrated spirometer operated by trained staff is essential.Ideally, examinations during employment should take place at thesame time of day to allow for diurnal variation and should correspondas closely as possible to the times of diisocyanate exposure. A fallof greater than 0.25 l on the mean corrected FEV1, measured on twoseparate occasions after allowing for the ageing effect, is consideredsignificant. It may also be useful to measure flow rate versus lungvolume (a flow–volume loop), which can help in identifying abnormallung functions.

Conduct of medicalexaminationsAny scheme must take account of localregulatory requirements. The exam-inations are best conducted by aphysician with training and experiencein occupational medicine. Whilst themeasurement of peak flows at inter-vals throughout the working day isuseful in diagnosing occupationally-related bronchoconstrictive problems

(see Part 3, Health: Diagnosis of diisocyanate asthma), it is not of particu-lar value in the routine screening of an asymptomatic individual. Records ofmedical surveillance should be retained. For example, a retention period of40 years is required under the relevant regulations in the UK (HSE, 1998).

The pre-placement examination may identify subjects suffering from hayfever, recurrent acute bronchitis, pulmonary tuberculosis, asthma, chronic bron-chitis or interstitial pulmonary fibrosis, whatever their cause, occupational orotherwise. The physician may decide that, because of the pre-existing disease,an individual could be at particular risk from additional exposure to chemicalsin the expected work environment. In this situation the physician may decidethat the potential additional risks should be fully explained so that the subjectcan make an informed decision about the type of employment most suitablein his or her own circumstances.

If, on routine surveillance examination, signs and symptoms of asthma arenoted (see Part 3, Health), the physician should investigate the causes withoutdelay. It may be recommended that the individual be relocated to another jobwhere there is no possibility of further diisocyanate exposure.

Key Theme 3: Neutralization, decontamination and disposal of wastes

In this text, neutralization means treating MDI or TDI with a solid or liq-uid neutralizer to destroy the isocyanate groups and hence minimize exposure


of humans or the environment. Decontamination means removing all tracesof these diisocyanates from the given surface or area. These topics are dis-cussed in the contexts of the routine cleaning of machinery and drums and ofaccidental spillage. It is important to understand the key principles of neutral-ization and decontamination, otherwise new problems may be created duringthe cleaning process.

There are potential problems associated with the process of neutralization.The liberation of carbon dioxide and heat can lead to drum rupture if the drumsused for neutralization are sealed before the neutralization reaction is fullycompleted. Ammonia-based neutralizers can lead to over-exposure to ammonia.Use of a neutralization formula containing a strong alkali may accelerate theformation of diamines from diisocyanates, and this needs to be taken intoaccount when disposal of neutralization residues is considered.

Types of neutralizerAbsorbent material/solid neutralizers

• Wet sand.• Wet earth.• Other inorganic materials such as kieselguhr, ‘kitty litter’ (which is gran-

ulated clay) or proprietary absorbents. Fuller’s earth is sometimes recom-mended, but has the disadvantage that it will turn to a mud-like consistencywhen mixed with water.

• Wet sawdust is useful for dealing with minor spills on floors. Dry sawdustmay sometimes be a fire risk, particularly in large quantities.

Liquid neutralizersNeutral

• Water and surfactant (surface active agent): the use of surfactant allows betterdispersion of water with MDI and TDI, which are immiscible with water.

Alkaline

• Water, surfactant and sodium carbonate: this mixture reacts faster than waterand surfactant alone.

CautionConcentratedaqueous ammoniais subject to anoccupationalexposure limit,and precautionsshould be taken toavoid inhaling thetoxic vapours. Thisneutralizer mayalso cause a veryfast neutralizationreaction, so do notuse it in closedcontainers orconfined spaces.

• Water, surfactant and ammonia: this reacts faster than a mixture consistingof water, surfactant and sodium carbonate.

• Water, and an alcohol (for example, isopropanol) and ammonia.

Routine cleaning of equipment and drumsCleaning of equipmentAny diisocyanate in the equipment will need to be neutralized; polyurethaneor polyurea deposits may also need to be removed. Polyurethane deposits maybuild up in some equipment, for example in mixing heads. Polyureas maybe formed in equipment that has been dismantled for subsequent cleaning ifleft open to atmospheric moisture. One neutralizer that may be used contains


industrial alcohol: this should be adequate for parts that are contaminated onlywith the unreacted diisocyanates. More vigorous decontamination proceduresmay be needed in some situations and it may be necessary to use highly polarorganic solvents such as dimethylsulphoxide (DMSO), dimethylformamide(DMF), or N -methylpyrrolidone (NMP). In the case of very bad contamination,molten salt baths or even surface blasting of components may be useful. Theblasting agent should be chosen so as not to damage engineered surfaces. Forall these cleaning processes, there should be no exposure of humans to the sys-tems. The suppliers of chemicals and equipment should be consulted to ensurethat recommendations for safe cleaning practices are obtained. Disposal of sol-vents containing diisocyanates, whether from routine solvent flushing of mixingheads or from separate cleaning of machine parts, should be in accordance withinstructions from the suppliers and with local or regulatory requirements.

Drum cleaningHere it is necessary to consider the disposal both of drums which are drip-freeand of drums which contain considerable quantities of unusable products suchas material used for cleaning machine lines. There are significant differencesin the handling of these, according to regulations and the availability of localspecialist facilities. These topics are discussed in greater detail in Part 2, Theworkplace: storage and use of MDI and TDI.

Drum decontamination and disposalWhen drums have been pumped out or drained to leave as little residue aspossible, there are two possible approaches (see Part 2, The workplace: storageand use of MDI and TDI for further details):

• Seal the drum immediately and send to a drum-handling specialist.• Decontaminate the drum using a slow reacting water-based neutralizer. On

no account should fast reacting systems be used or catalyst added. The drumshould be partially filled with neutralizer Formulation 1 or 5. One to oneand a half litres (approximately a quarter to a half a US gallon) should besufficient (ISOPA, 1997a). The following sequence can be used.

Drain drum until drip-free

Add neutralizer

Roll closed drum immediately at least four times

Open drum (CAUTION: excess pressure may be present!)and leave with a loose-fitting lid until all the reactionis completed

Close drum and dispose of contents and drum in approved manner


Polymeric MDI and TDI can be neutralized at about 25 ◦C. Higher viscositymaterials, such as some modified MDIs and TDIs, may need to be warmed togive low enough viscosities to allow mixing with the neutralizer.

Disposal of large quantities of diisocyanateThe disposal of large quantities of MDI or TDI should normally be undertakenonly by a specialist contractor. If, however, it is necessary to dispose of up toa drum full of diisocyanate this should be undertaken with extreme caution,and expert advice should be sought.

There are two problems that may arise in neutralizing diisocyanates in bulk:

• Contaminants in the diisocyanate may cause a very rapid reaction to takeplace, with the liberation of carbon dioxide gas.

Rapid reaction may occurduring the decontaminationprocess, Elastogran (1997).

• Incomplete neutralization may occur because of inadequate mixing of theneutralizer and the diisocyanate. The diisocyanate is about 25 % denser thanwater so that even if there has been drum rolling to mix the diisocyanate andwater, two layers will form once the drum is stationary. In that situation abarrier of solid polyureas will form, separating the two layers. This may thenlead to large quantities of diisocyanate not being neutralized even thoughthere was an adequate quantity of neutralizer in the drum.

It is important that large quantities of unusable MDI or TDI are notneutralized in a drum by adding liquid neutralizer to the diisocyanate.Diisocyanate should be added to the neutralizer with stirring, and notvice versa. The scale of such reactions should be reduced by dividing thecontents into several small quantities before neutralization, if no other way ofdisposal is possible.

Any attempt atneutralization of largequantities of diisocyanate,even if the material isdivided into smallerportions, could beconstrued by someregulators as wastetreatment operations,which require a govern-ment licence.

Disposal of diisocyanates as ‘polyurethanes’It was common practice to neutralize diisocyanates by adding wastediisocyanates to excess polyol (or polyol blend) to form polyurethane polymer,which was then disposed of (as landfill, for example). This approach isnot recommended for two reasons. Firstly, since the approach leads toover-neutralization of the diisocyanate there will be an excess of polyolor polyol blend, which may cause pollution problems. Secondly, if polyolblend (including catalyst) is used, there may be a violent reaction during theneutralization process.

There is one situation in which polyurethane formation may be used effec-tively to neutralize excess diisocyanate. It is not unusual for excess diisocyanateto arise from metering trials. Typically both polyol blend and diisocyanate aremetered together in the required ratio for complete reaction. Under such cir-cumstances it is reasonable to mix the two (polyol blend and diisocyanate)metering shots together to form polyurethane. However, this should be doneon a scale that excludes the possibility of violent reaction.

It should be emphasized that any polyurethanes produced in the neutraliza-tion processes above may be very crude, because the critical mixing conditionswhich are normal to polyurethane production are not observed.


Labelling of decontaminated drumsLabelling of containers is always important. Original labels should be keptintact. Once a drum has been decontaminated, a further label should be added.An example is given below. National, regional or local regulations will deter-mine the labelling of such drums. MDI and TDI may require different labels.

This drum has been decontaminated using. . .

The product contained in this drum should not be allowed to come intocontact with soil or the aquatic environment.

Name of the decontaminating company

date: signature:

Disposal of decontamination residuesWastes from decontamination procedures should be sent to specialist disposalcompanies, who will use incineration or landfill according to national, regionalor local requirements. The representatives of MDI and TDI suppliers may beable to give contact addresses. There should be discussions with contractors tobe sure that they are licensed according to local and national regulations andthat they use lawful and safe means of disposal.

Neutralization after a spillage

Spillages may be contained by bunding (diking) in areas where losses may beforeseen: such areas include pump or tank areas, where maintenance work iscommon. Where spillages are in other areas they can be isolated by temporarybarriers such as spill pillows or other devices. Materials which can be usedfor containment are wet sand, wet soil or wet sawdust. These can be usednot only to contain the spillage but at the same time to adsorb and partiallyneutralize the diisocyanate because it reacts with water in these materials. KeyTheme 6: Dealing with accidents gives further details of what to do in theevent of spillage.

FloorsThe main considerations here are that large volumes of spilled MDI or TDImay need to be handled, and that there may be significant contamination ofporous or cracked floors before neutralizer is applied. A floor would normallyserve as a heat sink, so a fast-reacting neutralizer may be used. However,ammonia-based neutralizers should be used only if ventilation is very efficientand/or emergency staff have air-supplied breathing apparatus.


Dealing with contaminated floors

• Absorb and neutralize diisocyanates on the floor using wet sand, wetearth, wet sawdust or proprietary absorbent. Add liquid neutralizer (For-mulation 1, 2 or 3, below).

• Clean up the area. See Disposal of decontamination residues above.• Add further liquid neutralizer and solid absorbent to the floor until air

monitoring shows that no diisocyanate remains in the floor material.• Avoid using ammonia-based neutralizer unless there is good ventilation.

A heavy-duty brush may be used to sweep the absorbent into the spill.After use, the brush should be placed in a plastic bag and then be disposed ofproperly, for example by incineration. An operator wearing suitable protectiveequipment should transfer the residues containing the diisocyanate to an opendrum. Liquid neutralizer mixture should be added to the solid residues inthe drum even if the solid was previously wetted with neutralizer. Sufficientshould be used to give a considerable excess of neutralizer solution over theamount of diisocyanate estimated to be in the spill. This mixture of solid andliquid should be stirred occasionally, monitored for temperature build-up, andshould stand for 1–2 days in a well ventilated place or outdoors to ensurethat the diisocyanate has fully reacted. The container can then be sealed. Awaste contractor should dispose of the residues by incineration or by landfillaccording to regulations or local practices.

Soil, water or roadwayThis section refers to spillages outdoors, as associated with transportationaccidents or storage tank failures. The key consideration is the protection ofpersonnel, after which the diisocyanate should be contained to prevent run-offto drains or inaccessible areas. Although the environmental impact of MDIor TDI on air, soil or water is rather low, exposure should be minimized.Diisocyanates in water or soil are neutralized by the water and soil compo-nents, essentially to form polyureas which are biologically and chemicallyinert. However, the diisocyanate should be cleaned up in a rigorous way.

SoilWhere material has been spilled onto soil and absorbed, it will slowly becomeneutralized with the formation of solid polyureas. The contaminated soil mayneed to be removed to an area for neutralization and testing before being sentto landfill or incineration depending on regulations or local practices.

WaterDiisocyanates are immiscible with, and significantly denser than, water andthus will drop to the bottom of a pool or river. However, in highly turbulentconditions there may be some local distribution of globules of material. Thediisocyanate will react once it is in contact with water. The rate of reaction


depends upon the specific diisocyanate, the water temperature and the degreeof subdivision of the mass of diisocyanate. Usually, the reaction is rather slow,taking days or even weeks, especially as some diisocyanate may be trappedwithin the solid waxy mass which forms from the diisocyanate on reaction withwater. Most of the reacted material, which is predominantly agglomerates ofpolyureas, remains submerged in water. However, sometimes these masses ofpolyureas may rise to the surface of the water due to trapping of carbon dioxideliberated in the reaction. Reacted material can be removed from the water byskimming the surface and dredging the bottom.

RoadwayWhere MDI or TDI is spilled onto a road or similar surface, it will need tobe isolated by surrounding with absorbent material. The diisocyanate can beneutralized by a covering of wet soil or sand, to which may be added alkalidecontaminant (Formulation 2). Ammonia-based formulations should be usedonly if nonessential personnel have been excluded and/or there is significantair movement to disperse the ammonia gas. It is extremely likely that the diiso-cyanate will have penetrated the surface of the road. A further application orseries of applications of neutralizer will be necessary until monitoring indicatesthat there is complete decontamination of the surface.

It is possible that spillages of pure MDI or of TDI may solidify on contactinga cold road surface. In such cases it will be necessary to remove this solid mate-rial from the road and then to mix it with absorbent/neutralizer mechanically.The road surface may need to be sandblasted to remove all the diisocyanate. Inthis case, the contaminated sand must be collected for subsequent neutralizationand disposal. Respiratory protection is necessary.

ClothingContaminated clothing should be removed immediately and put into animpermeable bag. If there is any doubt about the presence of free residualdiisocyanate the clothing must be decontaminated by soaking in neutralizersolution overnight. Depending upon the degree of spillage and any subsequentstiffening of the fabric, clothing may be disposed of or laundered by anindustrial contractor.

Minor splashes on overalls/coveralls and other clothes are likely to be neu-tralized by moisture in the fabrics and may be laundered normally.

Treatment of contaminated clothing

• Soak clothing in liquid neutralizer (Formulation 1, 2 or 3).• Leave overnight if contamination is excessive.• Launder normally, wash separately from other clothing.• Do not use ammonia-based solutions (Formulation 3), unless in a ven-

tilated area.

It is an advantage to wear front-fastening overalls and shirts, so that diiso-cyanate spillages are not drawn across the face when the garments are removed.


Snap fasteners, instead of buttons, are ideal for rapid removal of overalls.Contaminated clothing may affect support personnel such as first aiders andphysicians, unless precautions are taken.

Contaminated personal protective equipmentAfter contamination, protective equipment such as safety glasses, respiratorface pieces and other reusable safety equipment should be decontaminated.Equipment may be cleaned by wiping it with absorbent cloths soaked inneutralizer, which themselves must be decontaminated by immersing in aneutralizer solution before disposal. Badly contaminated equipment can beimmersed in neutralizer solution prior to disposal.

Neutralizer formulations

Liquid formulation without alkalisFormulation 1surfactant 1 % to 20 %water to make up to 100 %

There is no comprehensive work that is able to define a ‘best formulation’of surfactant and water. However, some preliminary work with TDI (Kiestler,1999) suggested that higher concentrations of surfactant lead to a faster overalldisappearance of TDI, and that ethoxylated surfactants were superior to anionicsurfactants.

Liquid formulations containing alkalisFormulation 2liquid surfactant 0.2 % to 2 %sodium carbonate 5 % to 10 %water to make up to 100 %

Formulation 3liquid surfactant 0.2 % to 2 %concentrated ammonia 3 % to 8 %water to make up to 100 %

Formulation 4ethanol or other alcohol 50 %concentrated ammonia 5 %water to make up to 100 %

In situations when protective equipment, tools, or machine parts are to bedecontaminated, or when the ambient temperature is freezing, there is advan-tage in adding an alcohol such as ethanol (industrial spirit), isopropanol orbutanol to the formulation. Up to 50 % of solvent is recommended depend-ing on the circumstances. The use of alcohols in the formulations means thatthe neutralizers will be flammable and that appropriate precautions will benecessary to avoid all sources of ignition or overheating.


Formulation 5liquid/yellow soap (potassium

soap with 15 % surfactant)2 %

polyethylene glycol (PEG 400) 35 %water to make up to 100 %

This is particularly useful for drums.

Key Theme 4: Using personal protective equipment

The polyurethane industry employs a wide diversity of processes and activi-ties that demand different systems of control for minimizing exposure to MDIand TDI. In all instances the first priority should be to minimize exposureby the use of appropriate engineering measures, including enclosure and theprovision of suitable ventilation, rather than to rely on personal protectiveequipment. In workplaces in which engineering measures and adequateventilation are provided, it should not be necessary for workers to usebreathing apparatus and to wear protective clothing beyond that nor-mally used in the general chemical industry. When suitable engineeringmeasures are not available, for example during some maintenance work orwhen spraying externally, the protective equipment will need to be matchedto the expected diisocyanate exposure situations. It is important that protec-tive equipment

• protects those parts of the body most liable to exposure, especially the lungs;• is comfortable enough to be worn properly for long periods;• provides adequate resistance to penetration (not necessarily perfect imper-

meability).

Personal protection needed for use with MDI or TDI can be selected fromranges of equipment already available to the chemical industry.

Normal operations

In many workplace environments, personal protective equipment will need totake account of the possibility of spills and splashes of liquid diisocyanatesonto the skin or into the eyes and, if necessary, protection of the airways frominhalation of vapour or aerosol if engineering measures cannot be applied ina particular situation (API, 2001a, 2001b). Contaminated surfaces can also bea source of exposure to diisocyanates. Respiratory protective equipment willusually not be necessary in well-controlled workplace environments. However,when maintenance or repair work is taking place, those involved may requirerespiratory protection, unless it is known that diisocyanate exposure is belowa concentration that may cause harm. Respiratory protection will be neces-sary when carrying out spraying operations externally, and also when sprayinginternally in the absence of proper spray containment and removal facilities.Respiratory protection should also be used when heating diisocyanates.

It is important to note that all the chemicals to which workers may beexposed in a particular workplace need to be taken into consideration when


selecting protective equipment. Chemicals that will often be found in work-places handling diisocyanates are solvents, release agents, catalysts and chem-icals provided for the neutralization of diisocyanates. Chemicals may well alsobe present for nonpolyurethane activities.

The selection of personal protective equipment depends on many factorssuch as:

• job demands (heavy or light wear, manual dexterity);• degree of exposure (light or occasional, to severe);• duration of exposure/wear time;• physical fitness of the wearer.

Personal protective equipment must be in good condition. It should be notedthat this equipment may deteriorate on storage or as a result of extended use.It may have been misused or subject to abrasion. As a result it frequentlyperforms less effectively in practice than in laboratory tests. The reasons forthe correct use of personal protective equipment may be forgotten, and careshould be taken to ensure that best practices become commonplace.

In most workplace situations where care is taken to minimize exposure,the protective equipment that is necessary may consist of some or all ofthe following:

• body protection overalls (coveralls);• eye protection safety glasses, face shield or goggles;• hand protection gloves;• foot protection boots;• respiratory protection breathing equipment.

There may be a need to wear additional protective equipment other than thatnecessary for protection against chemicals. For example, safety helmets (hardhats) may be mandatory for certain jobs and it may be sensible to wear animpermeable apron if splashes are expected.

Emergency situations

Dedicated equipment for use in emergency situations must be in locationsthat are accessible, clearly marked and known to those who may have touse it. Since emergency equipment will be used only very infrequently, it isimportant that training is provided at intervals to ensure that workers remaincompetent in its use. Respirators for emergency use should be maintainedregularly to ensure that they are fully functional at all times. There may beregulations defining the frequency of maintenance.

Escape from an incidentThe main requirement is to provide breathing protection for a short periodof time only. Cartridge respirators are suitable for emergency escape; the car-tridges should be replaced after use since there can be no way of knowing theamount of diisocyanate that the cartridge has absorbed.


Dealing with an emergency situationFull protective equipment may be required in the case of even minor workplaceincidents. For example, if a pipe leaks during unloading, then full protectionwill be needed (Figure 2.5). Full protective equipment will usually consist of:

Key Theme 6: Dealingwith accidents

• a chemical suit, or an impermeable overall with hood;• impermeable gloves;• impermeable boots;• respiratory protection suitable for extended use, for example a positive

pressure breathing apparatus with full face mask which is supplied byair cylinders.

Figure 2.5 Dealing with a diisocyanate spillage

Selection of personal protective equipment

A choice of equipment is needed to allow for individual preference, personal fit(different makers use different standard sizing systems) and different demandsof the job. Care should be taken to match the level of protection provided to thepotential exposure to the chemicals. The training should particularly emphasizethe importance of fitting the equipment to the person. Correct training shouldensure that the wearing of personal protective equipment does not make the


worker think that he is safe in all situations. This can lead to unsafe practiceswhich can be hazardous to the wearer and to other workers. The objective inselecting equipment is to provide acceptable and comfortable equipment witha reasonable degree of protection for short exposures, rather than excellentprotection in equipment which is very uncomfortable and may even be dis-carded. Equally, it is unreasonable, and might introduce other risks, to expecta worker to wear heavy protective clothing, especially in hot conditions. In hotconditions some workers leave suits unfastened, or even tear out the sleeves.If the conditions of the plant are such that heavy equipment has to be wornfor long periods during normal operations, it is an indication that the processneeds better design.

An excessively wide range of available equipment options may increase thelikelihood of mistakes in issuing equipment for specific jobs. Employers willnot want to carry a wide range of equipment anyway, and will find it simplerto over-specify the protection needed for some jobs in order to eliminate somestock items. Where personal protective equipment is required and provided, itshould not be just to the minimum theoretically required standard.

Air line systems, in which breathing air is supplied by lines throughout thefactory, generally give a higher standard of respiratory protection than air-purifying respirators and, after the initial cost of the air distribution supply,they are cheaper to maintain and run. Powered cartridge systems cost more,and need more maintenance, than unpowered systems, but they are generallymore comfortable and more likely to be worn correctly.

Protective clothingAny protective clothing must be removed with care after use to ensure thatthe wearer does not become contaminated. Any contaminated items must becleaned or disposed of safely.

Body protectionLong sleeved garments are preferred in order to protect the arms from skincontamination. Overalls/coveralls should preferably be made from heavy cot-ton or a laminated material and should provide protection to the wearer formore than 8 h. Many laminates of PVC, neoprene and polyurethane performedwell in permeation and penetration tests with MDI and TDI, and uncoatedmaterials were less effective. Solvents can affect permeation times markedly

Permeation testing onprotective clothingSPI (1994a, 1994b); Robertand Hayward (1999); Robertet al. (2000).

and diisocyanate may well be carried through the material with the solvent.Disposable clothing suitable for the chemical industry, even if offering

shorter protection times, is often preferred because of the difficulty of decon-taminating other types of protective clothing. Garments which are providedwith snap or Velcro –type fastenings allow fast removal of contaminatedclothing in an emergency.

It may be thought that a full body suit in an impervious material wouldprovide complete protection. However, this approach can be wrong on severalcounts. Almost no garment is fully impervious, and if it were the wearer wouldsuffer heat stress. In practice, except in the most specialized air-supplied suits,air permeates through the fabric, leaks through the fastenings or is pumped bybody movement in and out of cuffs at neck, wrist and ankle.


Eye protectionEye protection is often mandatory in the workplace to protect workers from avariety of hazards such as splashes from diisocyanates. Safety glasses, a faceshield or goggles are normally adequate for light duties. The operator shouldwear a full-face breathing apparatus or air line hood if the job involves a highrisk of splashing or releases of jets and sprays of liquid diisocyanates. Careshould be taken to ensure that eye protection is not handled with contami-nated gloves.

Hand protectionHand protection may need to be worn in many operations to prevent contactwith any contaminated surfaces. Care is required in choosing gloves appropri-ate to the job in terms of wear resistance and resistance to chemical contact.There are virtues in selecting robust gloves of moderate resistance to diiso-cyanates, and changing frequently to a new pair. Gloves have been tested fortheir resistance to diisocyanates. Information is available on a wide varietyof glove materials and proprietary designs (SPI, 1994a, 1994b). Nitrile rubbershowed excellent resistance to polymeric MDI and TDI; butyl rubber, neo-prene and PVC were also effective. Natural rubber and polyethylene did lesswell, but were likely to be satisfactory for light, precise work of short duration.Light-duty nitrile rubber gloves allowed good manual dexterity. Solvents cansignificantly reduce the protective ability of gloves to diisocyanates (Robertand Hayward, 1999; Robert et al., 2000). Diisocyanates can cause imperviouscoatings to harden and crack. Gloves should be replaced if this happens. Thetouching of unprotected skin with contaminated gloves can cause problems,and the source of such exposure is not always recognized.

Foot protectionFeet should be protected from splashing, and safety boots provide adequateprotection on normal polyurethane processing plants. However, rubber bootsmay be more suitable for decontamination after spillages. Cost is not a reliableguide to durability or resistance to permeation by diisocyanates.

Respiratory protection

Air can be supplied to the user through full-face masks, half-masks, visors,hoods, helmets and blouses (half-suits). Specialist advice should be obtainedin selecting the best form of equipment for a particular situation. Figure 2.6illustrates the main types of respiratory protective equipment for diisocyanates.

The use of respiratory protective equipment must be considered in situa-tions in which the levels of diisocyanate cannot be controlled to below theregulatory limits, for example during maintenance activities. Equipment forrespiratory protection is covered by regulations in many countries, and theseshould be consulted if there is any doubt about equipment suitable for usewith diisocyanates. There are well-developed standards for respiratory protec-tive equipment in most parts of the world. They usually refer to sizing, fit tests,face seal leakage, construction and other general features. Performance tests


Air purifyingequipment

Air line fedequipment

Self containedpressure-demandor positivepressurebreathingapparatus withfull facepiece

Figure 2.6 Types of respiratory protection

normally specify simple test substances which do not include diisocyanates.It is also necessary to consider the effect of airborne substances (in particularacid and solvent vapours) on the sensitive working parts, especially valves andseals that can harden or degrade in storage or use.

There are several studies indicating that much respiratory protective equip-ment can fall seriously short of the performance suggested by face-seal leakagetests or by tests on the filter cartridge alone. In most tests, the human subjectsare selected to exclude those for whom a good face fit is difficult to achieve.The quality of fit may be important to performance. People do vary, however,and equipment will not fit all equally well. Where the tests include move-ment and speech, the tests are limited in duration and do not usually includesevere bodily exertion or severe cross-draughts. Hence the quoted parame-ters (Total Inward Leakage, Nominal Protection Factor or Assigned ProtectionFactor) may not represent performance in practice, most commonly because


the equipment performs worse in practice than in the standard protocol in thetest room. The degree of protection afforded by air-supplied or air-cleaningdevices varies greatly (even several hundred fold) with the type of face piece.

Respiratory protection can affect visibility, both downward past the air maskand often to the sides; also communication can be difficult. A feeling of claus-trophobia or confinement can affect some workers.

Equipment for respiratory protection in workplaces should be stored in aclean, dry, easily accessible area and should be subject to regular, periodicinspection and maintenance to ensure that it is fully functional at all times.Training and refresher training in the usage of the equipment is necessarybecause the equipment may be used only very infrequently.

Some masks give no protection

Simple gauze or thin paper masks (‘nuisance dust masks’) that are com-monly available to reduce the level of particulates breathed in offer noprotection against diisocyanate vapour and aerosols. They must never beused to protect against airborne MDI or TDI.

Respiratory protective equipment falls into two categories (Figure 2.7):

Respiratory protective equipment

Air-supplied equipment Air-purifying equipment

Figure 2.7 Major classes of respiratory protective equipment

• Air-supplied equipment provides uncontaminated breathing air from an airline or a cylinder.

• Air-purifying equipment cleans the atmosphere before supplying it to thewearer. Renewable cartridges (also known as canisters) perform the cleaning.

Air-supplied equipmentThere are many types of air-supplied equipment (Figure 2.8). Some regulatorsspecify air-supplied equipment with full face piece, operated in a positive-pressure demand mode, or air-supplied face piece, helmet or hood, operatedin a continuous flow mode for use with diisocyanates. The air may be sup-plied through an air line or may be supplied from cylinders in self-containedequipment. These systems can restrict movement and air lines may provide atripping hazard. There is usually no means of warning the wearer if the airsupply fails for any reason.

Fresh air hose supplied systems comprise a mask with a trailing wide-boretube. However, it may be difficult to know whether the intake of the tube isdrawing in clean air. Supplied compressed air is usually preferred as the quality


Air supply

Air line

Half-masks

Air cylinders

Compressed airFresh airhose

Full-facemasks Full-face

masks

Full-face masks

Blouses (half-suits)

Full protective suits

Hoods and helmets

Visors

Figure 2.8 Sources of air supply in air-supplied equipment

can be better controlled. For jobs in which great mobility from a compressedair supply point is not required, a trailing uncoiled hose delivering compressedair to a hood or full-face mask is satisfactory. Although coiled air lines lookneater, they may be subject to tangling. Cylinder fed breathing equipmentshould be available (Figure 2.9) for use as emergency breathing equipment,for example, for cleaning up large spills and for fire fighting. This specializedequipment is heavy and personnel training is required before it can be used.Cylinders have a limited supply of air and cannot be used over long periodsof time. Some standards are available on the quality of air suitable for usewith breathing equipment (for example, see US OSHA Respiratory ProtectionStandard 1910.134). It is imperative that normal factory compressed air, whichmay contain oil droplets, should not be used.

Examples of suitable air line fed equipment are shown in Figure 2.10. Bothair line and cylinder supplies can be used to provide air to the wearer eitheras a constant flow, or on demand.

• Constant flow. A constant flow of air is simple to provide and use, but resultsin a large air usage. Cylinders are very rarely suitable for the provision ofconstant flow air, as their contents are soon exhausted. Constant flow systemsinclude full-face mask, hood, blouse or ventilated visor types. The extensivegaps around a visor make this type suitable only for low risk work.

• On demand. Positive-pressure demand equipment is based on a tight fittingface piece, inside which a pressure slightly above atmospheric is main-tained. When the wearer inhales, the demand valve opens before the maskpressure drops to atmospheric. Equipment of this type should be used when-ever the highest standard of protection is needed. Negative-pressure demandequipment, in which the valve does not open until the mask pressure isreduced below ambient pressure by inhalation, may allow the possibility


Exhalationvalve housing

Pressuregauge

Compressed aircylinder

Demand valve

Figure 2.9 Self-contained breathing apparatus (SCBA). Adapted with permis-sion from Respiratory Protective Equipment: a Practical Guide for Users (UKHSE, 1990)

of inward leakage. Air-supplied constant flow systems, or positive-pressuredemand valve systems, should always be used for spraying when there isno engineering control of aerosols.

Air-purifying equipmentThis type of equipment incorporates air-purifying cartridges, but has no inde-pendent air supply. According to the design, the cartridge may remove fromthe surrounding atmosphere vapours, or particulates including aerosols, or bothvapours and particulates together. The cartridges tend to be very efficient atabsorbing vapours or particulates until their capacity is exhausted and break-through occurs. Contrary to general expectations, gas-absorbing cartridgesare not necessarily efficient at removing particulates, and particulate-filteringdevices may not be efficient at removing gases. Dual function cartridges thatabsorb both gases and particulates are available and are most likely to besuitable for use in the presence of diisocyanates.

Equipment that relies on cartridges to purify the air has a serious limitation.In currently available equipment of this type, there is no end-of-service-lifeindicator for warning the wearer that the filter cartridge or canister is no


Lightweight air-fed visor

Compressed air line breathingapparatus incorporating

a full face mask

Figure 2.10 Air line fed breathing apparatus. Adapted with permission fromRespiratory Protective Equipment: a Practical Guide for Users (UK HSE, 1990)

Cartridges and filters: gases and aerosols

Gases and aerosols behave in different ways, and need to be removedfrom breathing air in different ways. A cartridge containing carbongranules is used to remove potentially harmful vapours. As the airpasses easily through the cartridge, vapours such as MDI or TDIdiffuse very rapidly onto the carbon, to which they adhere. Aerosolsdo not diffuse quickly and pass through the spacious air channelswith the air flow. A filter is used to capture the aerosols. The filtercomprises a thin mat of fibrous material that offers little resistance tothe breathing air flow, but provides a labyrinthine or tortuous routefor the air. The aerosols, which have much greater momentum thanindividual gas molecules, are deposited on the fibres as the air flowchanges direction.

longer effective for diisocyanates.Odour cannot be used as an indica-tor as the wearer cannot smell MDI orTDI until the concentration is greatlyin excess of permitted levels. Usersof cartridge-containing respiratory pro-tective equipment should understandthat any abnormal odour or irritationis evidence that the capacity of thecartridge is very much overloaded andshould have been replaced earlier. Therecognition of such warning propertiesmust, however, never be relied upon asthe mechanism for determining when a

cartridge should be changed. Effective change schedules must be established


and implemented by the employer. The employer may obtain relevant informa-tion from cartridge suppliers and other experts. It may be possible to use datathat have been determined by experimental work including ‘breakthrough time’studies, by mathematical predictive modelling and by workplace simulations.Whichever method is selected, the employer must implement a regular car-tridge change schedule based on the best information available (OSHA, 1998).Great care should be taken to ensure that the use of cartridges is confined toshort periods of time before they are changed, unless the life expectancy of thecartridge in that particular workplace situation has been established. The localregulatory situation and the potential exposure to a range of chemicals will needto be considered in selecting cartridge-type respiratory protective equipment.

Cartridges are usually colour coded to distinguish the suitability for removingdifferent classes of contaminants, for example organic vapours, ammonia andorganic amines, and particulates, including aerosols. Cartridges that are suitablefor removing diisocyanates are not usually identified as being solely for thatpurpose. Cartridges are nevertheless available that are suitable for diisocyanatevapours, diisocyanate aerosols and for a combination of both vapours andaerosols. The nomenclature for air purifying cartridges is not standard acrossthe world, and local advice must be sought if there is any doubt concerningthe correct cartridge or canister to be used. Further information is availablefrom manufacturers and regulators.

Cartridge-containing equipment falls into two classes, those that are lung-powered and those that have motor-driven pumps to pull the air through thecartridge (Figure 2.11).

Lung-poweredequipment

Motor-poweredequipment

Air-purifyingcartridge equipment

Half-masks

Full-face masks

Half-masks

Full-facemasks

Visors

Hoods andhelmets

Blouses(half-suits)

Figure 2.11 Types of cartridge-based respiratory equipment

Lung-powered respirators may employ a half-face mask, covering onlythe nose and mouth, or a full-face mask offering protection to the eyesalso (Figure 2.12). Lung-powered systems tend to be exhausting to wear forlong periods.


Figure 2.12 Lung-powered full face mask cartridge respiratory equipment.Adapted with permission from Respiratory Protective Equipment: a PracticalGuide for Users (UK HSE, 1990)

Battery pack

Fan/filter

Figure 2.13 Motor-powered full face mask cartridge respiratory equipment.Adapted with permission from Respiratory Protective Equipment: a PracticalGuide for Users (UK HSE, 1990)


Motor-powered versions (Figure 2.13) operate by pumping filtered air tothe wearer. Motor-powered respirators offer more versatility in face/head coversuch as:

• lightweight visor;• visor combined with safety helmet;• hood;• blouse (half-body, face and head protection).

The effectiveness of some typical air-purifying respirator cartridges in remov-ing MDI aerosols from air has been investigated. Organic vapour cartridgeswithout a particulate filter were not effective at removing MDI aerosols fromair, whilst organic vapour cartridges with filters for dusts/mists and high effi-ciency filters (HEPA) removed more than 99 % of MDI aerosol and vapour inall the atmospheres tested (Spence et al., 1997). Low breakthrough times ofvery fine MDI aerosols were found with those cartridges that were not designedto remove particulates (Table 2.4). Cartridges from different manufacturers didnot necessarily have equal efficiency at removing very small particles. Inter-estingly, in this study the formation of MDI aerosols was evident even at verylow (<100 µg/m3) total MDI concentrations.

Table 2.4 Cartridge breakthrough testing with spray-generated MDI aerosol.

Source of cartridge Cartridge type Breakthrough timemin

Manufacturer 1 Organic vapour/high >1440efficiency particulate

Manufacturer 2 Organic vapour/dust/mist >1440Manufacturer 1 Organic vapour/dust/mist 200Manufacturer 1 Organic vapour <10

Aerosol test atmospheres: 5300 to 9000 (mean 7300) µg/m3; mass median aerodynamicdiameter = 2 µm.Breakthrough time was defined as the time taken to reach a concentration of 1 ppb MDI.

Key Theme 5: Monitoring exposure

Why monitor levels of diisocyanates?

There are several reasons why a monitoring programme should be establishedin any workplace or site using diisocyanates:

• to ensure that workplace controls are fully operational and employee expo-sure is identified and minimized;

• to ensure that any releases from the site are identified and, when necessary,any exposure of the community and environment is controlled or eliminated;

• to demonstrate compliance with regulatory requirements.

What needs to be monitored?

In order to fulfil the norms of product stewardship and regulatory compliance,it may be necessary to monitor the following scenarios.


The workplace

• exposure of process workers, maintenance personnel, other workers andvisitors;

• changes of worker exposure with changes in workplace or process condi-tions;

• surface contamination;• exposure during and after spillages.

The community and the environment

• stack release levels;• fenceline concentrations;• exposure during and after spillages due to transport accidents.

Furthermore, it will be necessary to have programmes for the regular calibrationof analytical equipment.

How should monitoring be carried out?

The choice of a method of monitoring for MDI or TDI depends on a num-ber of factors, and selection of the method should always be undertaken withprofessional advice. A range of techniques is available for sampling and anal-ysis of diisocyanates, but all have limitations on their use. Knowledge ofthe situation in which monitoring is to be carried out is essential before achoice can be made. Determination of exposure depends on both represen-tative sampling and reliable analysis. Representative sampling depends onthe sampling strategy, on the positions at which sampling is carried out andon the correct use of the sampling device itself. Further details on the strat-egy of sampling will be found below in Part 2, The workplace: storage anduse of MDI and TDI. The analytical methods, and the factors which must betaken into account in making the choice, are discussed in Part 5.7, Samplingand analysis.

Factors that affect the choice of method include:

• The physical form of the diisocyanate. Depending on the nature of the oper-ation in the workplace, a diisocyanate may be present in the atmosphere asvapour, aerosol, or both, or even as a reacting mix with polyol blend. Ifthe samples of aerosols or vapour are not representative of what is presentin the air, the final result will not give an accurate indication of the expo-sure levels.

• The reason for which the monitoring is being undertaken. For example, ifthe purpose is to determine workplace exposure levels, it is important thatthe monitoring reflects as closely as possible the actual levels experiencedby personnel. Concentrations of diisocyanate in the workplace can varyconsiderably if there are air currents, and during certain steps in a routineoperation, for example during mould closure. There needs to be a clear


understanding of the difference between the results obtained from workplacearea monitoring (static monitors) and those from personal sampling deviceswhich sample the atmosphere in the breathing zone of the worker.

• Sampling conditions. Measurement of diisocyanate releases within an ex-haust stack must take into account factors such as other substances present,air speed, temperature and humidity.

Regulatory authorities differ in their requirements for the measurementof diisocyanate levels in the workplace. Some specify the limits to beachieved as concentrations of MDI or TDI. Other authorities expressthe limits in terms of the total reactive isocyanate group (TRIG) con-centration (see Part 5.6, Occupational exposure limits, stack limits andcommunity limits).

• Local regulatory requirements.There may be requirements as tothe method used to show com-pliance with occupational exposurelimits or to determine releases frompolyurethane production plants. Itmay be possible to use a methodother than the recommended one if

the chosen method can be shown to fulfil regulatory requirements.• The technical skills available. Some monitoring instruments can be oper-

ated fairly simply with little training required, while other methods requirea high level of analytical equipment and professional expertise. A combi-nation of methods of differing complexity, such as continuous paper tapemonitoring combined with a regulatory reference method, may be requiredto give a complete picture of exposure levels.

When should monitoring be carried out?

A regular programme of sampling and analysis should be established to buildup an understanding of the exposure of the workforce. The strategy for this isdiscussed below in Part 2, The workplace: storage and use of MDI and TDI.An alarm system based on continuous monitoring to detect raised levels ofairborne diisocyanates may be set up to cover areas of the plant where, forexample, high levels could be released if the ventilation failed.

It is essential that monitoring be carried out routinely and whenever

• a new process is established;• there have been changes to existing equipment or to a process;• health problems are suspected;• a leakage is suspected;• there has been a spillage or other incident involving release of diisocyanate,

to check the atmosphere before personnel can return to the area.

The establishing of a monitoring strategy will depend on the process andon regulatory requirements. Different monitoring equipment may be neededfor recording the different types of exposure levels. Advice on sampling andanalysis is available from diisocyanate suppliers, specialist analytical services,local regulatory authorities or instrument manufacturers.

Record-keeping is an essential part of all monitoring. Information should belogged on the date and time, the method used for monitoring, the position of thesampling, as well as the values obtained. Information from personal monitoring


must indicate the individual involved and the jobs being undertaken. Thereneeds to be an understanding of the relevant regulatory demands, which mayinclude statutory recording formats for the results of workplace monitoring.

Key Theme 6: Dealing with accidents

Accidents can happen

Accidents can happen even in the best-managed operations. Spillages occurfrom a variety of causes, and very occasionally incidents arise involving thedevelopment of excess pressure in containers. Major accidents involving MDIor TDI are fortunately very infrequent. It is, nevertheless, important to haveprocedures in place to deal with all these eventualities, however unlikely theymay be. It is necessary for all staff to receive periodic training on the correctprocedures to implement, and to be aware of the possible health implicationsof over-exposure to diisocyanates.

Most workplace releases of diisocyanates involve relatively minor spillagesor drips of diisocyanates that will be neutralized by the production or main-tenance staff involved. There should always be easy access to an adequatesupply of neutralization materials available in workplaces and the location ofthese materials should be clearly displayed. Supervisors should ensure that allincidents, however minor, are recorded so that procedures can be analysed andwhere necessary modified, or refresher training undertaken, to prevent recur-rence. Supervisors will also need to be aware of the possible delayed healtheffects that may occur if over-exposure has arisen.

In many organizations it will be necessary to have a designated emergencyteam which is able to take control in the event of a larger accident. Theteam should have links with the local emergency services who need to beaware of the location of storage vessels containing diisocyanates and otherchemicals. Contingency procedures for the containment and neutralization ofspills need to be discussed with them in case their help is required at anytime. The diisocyanate suppliers offer specialist advice and practical help inmany emergency situations, and have mutual aid networks in some countriesto give help and advice during an emergency. These services can be accessedat any time of day or night through telephone numbers given in the manu-facturers’ safety literature. See Part 2, Transport of MDI and TDI below forfurther details.

If the accident results in an individual breathing airborne diisocyanate, or ifthe person receives splashes on the skin or in the eyes, the first aid proceduressummarized below should be followed. The background to these procedures isdiscussed in Part 3. First aiders need to remember that exposure of themselvesmay still be a possibility and they may need to wear protective equipmentbefore helping others. If a local physician is called in to attend to an affectedindividual, or if hospital treatment is required, it is important that relevantinformation is provided to the medical staff. Ideally, the manufacturer’s safetydata sheet should be made available.


MDI or TDI: First aid

Breathing difficulties due to vapour, aerosol or MDI dust

• The person affected should be moved from risk of further exposure andmade to rest.

• Obtain medical attention immediately.• The onset of symptoms may occur several hours after exposure has

taken place.

Eye contamination

• Flush the eyes immediately with the contents of several sterile eye washbottles or copious amounts of tap water. Then remove contact lenses,if present and easily removable, and continue eye irrigation for not lessthan 15 minutes.

• Obtain medical attention.

Skin contamination

• Wash off thoroughly with large amounts of water and then wash wellwith soap and water.

Swallowing

• Do not induce vomiting.• Wash out the mouth with water.• The person affected should be made to rest.• Obtain medical attention.

Note for guidance of physicians

• MDI and TDI are respiratory irritants and potential respiratory sen-sitizers. There are no specific antidotes and treatment is essentiallysymptomatic for primary irritation or bronchospasm.

• MDI and TDI have very low oral toxicity.• Post-incident checks are needed.

Spillages

All spillages, however small, must be attended to immediately since there is arisk of over-exposure of those nearby. Most spillages involve relatively smallquantities of diisocyanates and arise, for example, from accidents during themaintenance of equipment or from a drum damaged during handling opera-tions. Much larger quantities may be released if a feed line bursts. Storagetanks may occasionally be overfilled, resulting in spillages, and hoses usedin the transfer of diisocyanates may become uncoupled. Transport accidentscan release large quantities of diisocyanates, and these can, of course, occurin situations far removed from a factory environment and experienced help


may not be available. In all situations, the actions that should be taken areessentially the same.

The principles to be adopted should be to protect people first, then to preventor minimize any releases to the environment, and finally to protect propertyand product.

1. Identify the material(s) involved.2. Evacuate from the immediate area everyone not essential to dealing with

the emergency and keep them upwind to avoid breathing vapour. Isolatethe area and prevent access. Remove ignition sources.

3. Notify the local emergency services and the management immediately ifthe spill cannot be handled by the available personnel. Call the supplier orthe emergency response number provided by the supplier for expert helpif needed.

4. Put on full personal protective equipment (suitable respiratory protection,face and eye protection, protective suit and gloves).

5. Control the source of the leak, where applicable. This may involve actionssuch as closing a valve in a supply line, or undertaking an emergency repairto a hole in a drum with a temporary bung or suitable adhesive tape.

6. Open doors and windows, if inside a building, to increase the ventilationand aid removal of diisocyanate vapours.

7. Contain the spill to prevent further spread of diisocyanate, when possiblealso absorbing the diisocyanate with sand, wet earth or absorbent clays(vermiculite or kieselguhr). Add neutralizer to the absorbent materials.Pump (using a drum pump) any diisocyanate liquid standing in pools intoclosed, but not sealed, containers that are clean and dry. Spill pillows canbe used for containing big spills. If the spillage is very extensive, coverthe spillage with fire fighting foam (for example 3 % protein) to minimizethe liberation of vapour. Whenever possible, prevent the material fromentering waterways or drains, including lakes, rivers, streams and sewers.If this happens, notify the water authorities immediately.

8. Neutralize the diisocyanate and decontaminate all surfaces and equipmentthat have been in contact. The procedures and formulations in Key Theme3: Neutralization, decontamination and disposal of wastes should be used.Isolate the residues for safe disposal.

9. Check, using analytical equipment, that the clean-up procedures have beeneffective and that decontamination has been successful. If the diisocyanatehas been in contact with a porous surface, or one with cracks or fissures,the decontamination procedure may not have been fully effective. If thespill occurs on a bitumen surface there may be some damage requiringrepair. There may be a slow release of further diisocyanate that will requireadditional attention, for example by covering with impermeable sheetingon top of a thin layer of further wet absorbent. Solidified diisocyanate maybe removed mechanically, including the use of sandblasting. If sandblast-ing is used, the contaminated sand must be collected, decontaminated anddisposed of in an approved manner.

10. Remove waste materials for incineration, for disposal by a specialist con-tractor or for landfill on approved sites. The choices will probably begoverned by local regulations.


11. Make a record of all accidents, and consider actions to prevent recurrence.Actions may include amendment of working procedures, improvement ofequipment and machinery, and improved training of those involved.

Actions following a spillage

• remove nonessential personnel;• inform management;• put on protective equipment;• contain spillage;• neutralize diisocyanate;• decontaminate surfaces;• isolate and dispose of waste;• monitor for residual diisocyanate;• record what has happened; take steps to prevent recurrence.

Emergency equipment

• personal protective equipment;• neutralizer;• empty drums;• absorbent material;• shovel and brush;• adhesive aluminium tape;• labels;• bungs;• equipment to monitor for diisocyanate.

Contamination of eyes, skin or hair by diisocyanateSee the First Aid advice for eye contamination. The key consideration is speed.Do not use any neutralizer solution in the eyes. Any splashes of diiso-cyanate on the skin should be removed as soon as possible by wiping withabsorbent material, followed by washing with soap and warm water. Con-taminated clothing must be removed and decontaminated as described in KeyTheme 3.

Study on skin decontamination

A study on removing polymeric MDI from the skin has shownthat water or soap and water were less effective than corn oil,polypropylene glycol (molecular weight about 700), or a commercialpolyglycol-based skin cleanser (Wester et al., 1998). Water, or soapand water, were decreasingly effective with time. Therefore cleaningsoon after contamination is important.

If spillage of a diisocyanate ontothe skin is not removed quickly itwill react with water in the skin, andpossibly with the skin itself, leavinga leathery deposit which cannot beeasily removed. The deposit will comeoff mechanically in due course. It isimportant to use cleaning materials thatwill not cause the diisocyanate to pass

through the skin. Many organic solvents, such as dimethylsulphoxide (DMSO),dimethylformamide (DMF) and acetone, will dissolve MDI or TDI. However,they should not be used for skin cleansing because they may cause


permeation of the diisocyanate into or through the skin and may have toxic ordefatting actions of their own. Proprietary skin cleaning agents may be used,but only if hygiene studies have shown them to be effective. Proprietary skinhygiene packs may contain both ‘indicator’ wipes to check whether the skinis contaminated, and neutralizer solution to clean contaminated skin.

Dealing with contaminated skin

Minor splashes

• Remove contaminated clothing.• Clean off excess diisocyanate from the skin immediately using dry tow-

els or other absorbent fabric. Then wash with clean warm water, or witha proprietary cleaning agent.

Drenching

• Remove contaminated clothing.• Shower without delay using soap, or a proprietary cleaning agent, to

wash off the diisocyanate. Do not remove respiratory protection (ifworn).

• DO NOT USE organic solvents or alkaline neutralizers.

If hair becomes contaminated with diisocyanate, towels should be used toabsorb as much of the material as possible. The hair should then be washedthoroughly with warm water. Mineral oil and/or petroleum jelly may aid theremoval of the diisocyanate. Any residual material may need to be removedby combing and possibly cutting off hair.

Further information on the effects of diisocyanates on the respiratory tract,the skin and the eyes can be found in Key Theme 2: Protecting health and inPart 3, Health.

Contamination of clothingIf clothing becomes contaminated following accidental release of diisocyanates,steps must be taken to avoid inhalation of vapours and to minimize trans-ferring diisocyanate to the skin or eyes. If the person wearing the contami-nated clothing requires first aid or medical attention, the helpers must avoidbecoming contaminated themselves and must avoid breathing diisocyanatevapour.

Contaminated absorbent clothing should be removed carefully, avoidingspreading diisocyanates to the face and minimizing diisocyanate inhalation.If the person is wearing respiratory protection this should not be removeduntil cleaning is complete. If the clothing is impermeable to diisocyanates, forexample a protective overall/coverall, showering should take place with theclothing and respiratory protection (if worn) left on. This will help to removethe diisocyanate and will minimize skin or respiratory contamination. If theshower is situated outside, steps should be taken to prevent it freezing in winter.


It is also important to note that TDI will crystallize if the water temperature isbelow 10 ◦C (50 ◦F), making its removal more difficult. Contaminated clothingshould be put into impermeable bags or containers prior to decontamination,and before laundering or disposal (see Key Theme 3: Neutralization, decon-tamination and disposal of wastes).

Modelling spillage scenariosModelling, using realistic assumptions for temperatures and weather condi-tions, has been used to estimate diisocyanate concentrations in accidentalreleases scenarios. Modelling by Robert and Roginski (1994) shows that con-centrations of MDI equivalent to 20 ppb are confined to the atmosphere directlyabove the spill. Because of its higher vapour pressure, TDI gives rise to con-centrations well in excess of 20 ppb some distance from the spill.

A different modelling exercise developed the following scenarios.

Scenario 1A hose ruptures when transferring MDI from a truck into a storage tank. Theflow is 15 m3/h (approximately 4000 US gallons/h) at a temperature of 30 ◦C(86 ◦F) and the release continues for 5 min. The diisocyanate forms a pool2 mm (0.08 inches) deep and 625 m2 (6700 ft2) in area.

Result: Because of the low vapour pressure of MDI at 30 ◦C, concentrationsof 20 ppb are confined to the atmosphere directly above the pool.

Scenario 2A 200 litre (55 US gallon) drum of TDI falls from a truck and has ruptured. Thetemperature of the liquid is 30 ◦C. The liquid covers an area 100 m2 (approxi-mately 1000 ft2) at a depth of 2 mm (0.08 inches).

Result: A concentration of 20 ppb of TDI could be attained at ground level90 m (approximately 300 ft) from the spill.

Examples of major accidents and their consequencesTwo case histories of major spills of TDI and one involving polymeric MDIare given below. It will be noted that no long-term adverse environmentaleffects were produced. A full discussion of the absence of significant long-term environmental impact from the diisocyanates on plant and aquatic lifecan be found in Part 4, The environment.

Case history 1. Spillage of TDI from a road tankerA road tanker containing 20 tonnes (44 000 lb) of TDI left the road, ran downan embankment and overturned. A valve was fractured and about 14 tonnes(30 000 lb) of material spilled from the tank before the leak could be stoppedby the fire services. The remaining TDI in the tanker was pumped out by thehaulage company, and the vehicle was decontaminated and removed.

The spilled material had spread out over an area of approximately 300 m2

(approximately 3000 ft2) of marshy woodland, through which ran a water ditch.


The TDI was prevented from entering this ditch by the digging of a barrier ditch1.5 m deep (approximately 5 ft), which was lined with polyethylene sheeting.The soil temperature of 5 to 10 ◦C (41 to 50 ◦F) caused the TDI to crystallizeafter a short time. About 12 h after the accident an operation was started tocover the area of the spillage with wet sand to a depth of 80 to 120 cm (approx-imately 31 to 47 inches). Most of the surface water and TDI was absorbed bythis covering layer, which was mixed mechanically. The layer of sand and soilwas not removed from the area in order to prevent possible contamination ofthe road surface by leaking TDI from the absorbent during transportation.

Samples of soil and water were taken from various points in the spillagearea, to measure the concentrations of TDI present. One week after the incidentTDI was detectable in the soil samples, but after 6 weeks the TDI had largelyreacted with the water. Samples taken one year later contained no detectableTDI or TDA (toluene diamine). The ground water was sampled over a periodof 5 years. No TDI or TDA was ever detected. Three months after the accidentthe vegetation was developing normally.

Case history 2. Spillage of TDI during the unloading of a shipA spillage of 40 tonnes of TDI occurred at a dock during the unloading of aship. As the ambient temperature was −20 ◦C (−4 ◦F), the TDI solidified andthere was no pollution of the water. The TDI, mixed with the surface layerof ice and soil, was mechanically shovelled into containers. The spillage areawas covered with clean sand.

Neutralization of the TDI was carried out in a mobile cement mixer usingaqueous ammonia before the ambient temperature rose. Neither TDI nor TDAcould be detected in the residues after this treatment.

Case history 3. Spillage of polymeric MDI during a rail accidentA train derailment involving several train tank cars resulted in a bridge failure.A rail tank car containing polymeric MDI was damaged and 50 tonnes of thediisocyanate were released, mainly into a river but also onto soil. A major firelasting 2 days occurred which involved the contents of some other tank cars.The MDI did not ignite. The river water was at a temperature of 4 ◦C (39 ◦F) atthe time of the spill, and 20 ◦C (68 ◦F) after 12 weeks. The MDI solidified intopartially-reacted floating lumps and sheets of polyureas, which were recoveredfrom the river by a floating barrier across the river and other means. MDI alsocollected on the river bed in areas of slow moving water. Material that wascollected from the river, together with contaminated soil, was removed fromthe site and incinerated. About 18 h after the spill, 20 ft (6 m) downwind, levelsof airborne MDI vapour were 2 to 4 ppb. The US Environmental ProtectionAgency declared the material in the river to be nonhazardous 3 days afterthe accident.

Development of excess pressure inside containersExcess pressure may arise in containers or storage vessels containing MDI orTDI due to contamination of the diisocyanate. If diisocyanate in a closed con-tainer such as a drum becomes contaminated with water, the reaction of waterand diisocyanate produces carbon dioxide, resulting in a build-up of pressure.


MDI and TDI react with water with the liberation of carbon dioxidegas. As both diisocyanates are immiscible with water, the rate of thereaction is slow when a two-phase system is present. The liberationof carbon dioxide will be much faster if the diisocyanates are finelydispersed, if there is a catalyst present (such as a tertiary amineor an alkali) or if a homogeneous mixture exists (e.g. when acommon solvent is present). Liberation of carbon dioxide can occurin homogeneous, catalysed mixtures within seconds.

The excess pressure can cause thecontents to be ejected in a vigorousstream or fountain when the containerruptures. Incidents have even beenrecorded in which bulging drums ofdiisocyanate have been propelled manymetres with great force by the suddenrelease of pressure following drumfailure. The best method for relieving

pressure in bulging drums will depend on the local situation. Chemicalsuppliers often have information on appropriate means of achieving this andshould be contacted when establishing the safety procedures on a site.

If a package is bulging because of excess internal pressure immediate actionshould be taken as indicated below.

For drums under low pressure (a slight bulging of the face of the drum tobelow the level of the top rim):

1. Wear personal protective equipment including full face, eye and respira-tory protection.

2. Slowly unscrew the bung to release pressure.3. Advise the supplier of the problem, particularly the condition of the seal

on delivery.

For drums under high pressure (face of drum bulging above the top rim):

1. Do not attempt to release the bung.2. Clear everyone from the area.3. Wear emergency protective equipment.4. Cover the drum with tarpaulins or other material.5. Isolate the drum if this is possible without risk. Care is needed as movement

may agitate the contents and accelerate the reaction.6. Contact the supplier for advice, or puncture the drum to release the pressure.

A drum can be punctured near its top and above the level of the liquidin the drum by means of a long lance or spike. A suitable device is shownin Figure 2.14. Detailed advice on how to undertake this operation will beavailable from the supplier of the diisocyanate. Whilst this operation is beingcarried out, all noninvolved staff must be evacuated from the area. Personnelinvolved must wear full protective equipment.

Pointed steelpin

Figure 2.14 Drum puncturing device


The punctured drum must be placed in a controlled area until any reactionhas finished, before being returned to the supplier as soon as possible forsafe disposal. For transport, the punctured drum should be placed inside anoverpack drum fitted with a pressure relief device. Further pressure build-upmust be avoided by regular venting.

If drums fall into water during an accident they should be inspected afterrecovery for leaks. In the absence of leaks they should be wiped dry andreturned to the supplier. Damaged or leaking drums must be suspected aspotentially contaminated with water, with the consequent possibility of a pres-sure increase. A ruptured or leaking drum should be turned so that its damagedarea is facing upwards. The drum should be covered to prevent the entry ofrain, dirt or other materials. Air-inflated compression belts may be used astemporary seals for split drums. Holes should be sealed temporarily using aresin-based metal repair kit or a wooden plug. Any spillage should be removedand neutralized. The diisocyanate in the drum should be pumped or drainedinto a clean, dry, undamaged drum. The damaged drum should then be decon-taminated before disposal.

If there is a leak in a stationary container such as a storage tank, it should bepatched temporarily, for example with adhesive tape. The contents should betransferred to a container, which should be blanketed with dry air or nitrogen.The new container should be monitored to ensure that no excess pressuredevelops from any moisture.

Very serious situations may occur if a polyol is inadvertently dischargedinto a diisocyanate storage vessel, or vice versa. If this occurs, an emergencysituation should be assumed to exist. The area should be evacuated, all stirringand circulation pumping stopped, the emergency services and the managementcalled, and the suppliers consulted. It will be important to vent the vesseland to keep the contents as cool as possible until it is judged that no furtherreaction will occur. This may take many days. Once this situation is reached,further steps will depend upon the nature of the reaction mass inside the ves-sel. Specialist advice may be required from the chemical suppliers to effectsatisfactory neutralization and decontamination procedures.

Incidents involving fire

MDI or TDI are not easily ignitable but may be involved in a fire causedor propagated by other materials. For polyurethane production facilities, thefire emergency planning and the precautions taken will depend very largelyon factors such as the type of buildings and the overall fire load. Emer-gency planning and fire precautions as they relate to the handling of per-sonnel, the involvement of the local fire service, and the location and typeof alarms, are based on a risk assessment of the whole facility, and so arebeyond the scope of this book. The following information is specific to MDIand TDI.

Fire behaviour and fire properties of MDI and TDIA review of reports on some 400 incidents involving MDI and TDI over30 years indicates that in no case has an incident been attributed to the ignition


of MDI or TDI, nor is there evidence that either has contributed to the propa-gation of the fire in any significant way.

The flash points and autoignition points of MDI and TDI are relatively high,and neither shows explosive properties, reflecting the difficulty of ignitingthese materials.

Detailed information onincidents, fire propertiesand fire behaviour is givenin Parts 4, 5.4 and 5.5,respectively.

There are other aspects of fire which have to be assessed, and classificationsof fire hazard have been introduced by a number of authorities. One scheme isthat of the widely referenced US National Fire Protection Association (NFPA).This addresses the health, flammability, instability and related hazards that arepresented by short-term exposure to the diisocyanates under conditions of fire,spillage or other emergencies. The proposed ratings for polymeric MDI, pureMDI and TDI (Collins et al., 2000) are given in Table 2.5. NFPA has indicatedthat the interaction of diisocyanate with water is not a significant hazard ina major fire situation. This is an important aspect of extinguishing fires, asindicated below.

Table 2.5 Proposed NFPA ratings: degrees of hazard.

Substance Health Flammability Chemicalreactivity

Specialhazards

PMDI 2 1 1 Not classifiedMDI 2 1 1 Not classifiedTDI 3 1 1 Not classified

Ratings

Health 2: can cause temporary incapacitation or residual injury underemergency conditions.

Health 3: can cause serious or permanent injury under emergency conditions.Flammability 1: substance requires considerable preheating under ambient

conditions before ignition or combustion can occur.Chemical

reactivity1: substance is normally stable but can become unstable at elevated

temperatures or pressures.

Special hazards relate to reactions under certain circumstances such as unusualreactivity to water, or oxidizing properties.

If a fire occursSmall fires involving diisocyanates should be extinguished using dry chem-ical or carbon dioxide appliances. Water should not be applied unless froma safe distance (e.g. by hoses) and in large quantities. Such fires are usuallydealt with by the local trained and equipped personnel.

Large fires involving diisocyanates can be extinguished with large vol-umes of water, as normally applied from a distance by hoses. Water-basedprotein or other fire-fighting foams can be effective in extinguishing such firesas well as suppressing the release of diisocyanate vapour: however, there havebeen cases where the time lost in obtaining such foams has led to more haz-ardous situations than would have arisen with the immediate use of water.

The local fire services should already have plans of the site showing areasof storage of MDI or TDI, so that they can take preventative action by cooling


these critical storage areas with water to prevent the explosion of metal drums,or the melting and degradation of combustible containers.

As in any fire situation, all nonessential members of the workforce shouldbe moved up-wind of the fire and only trained and well-equipped personnelallowed near to the fire until the fire service takes control of the situation.

Schupp (1999), in collaboration with an industrial fire service, undertookstudies which included extinguishing fires of MDI and TDI, using foam basedon water and detergent. The studies include details of the decontamination ofthe fire residues, as well as the analysis of gases from the two pools, beforeand during the fire.

Actions after a fire incidentImmediate actionThe first action is to have the area monitored for diisocyanates in the air. Onlyafter that should personnel be allowed on the site. A decision must be madeon how to remove residual MDI or TDI. This may be very difficult if largequantities of material of unknown condition are left. Collaboration with boththe diisocyanate manufacturers and fire services may be essential. Small quan-tities of diisocyanates should be neutralized by the methods given in Part 2,Key Theme 3. Fire residues and contaminated extinguishing waters should betested before disposal, in accordance with local regulations. Testing should beof both chemical and biological aspects of water quality. An example of a testreport is that of Cheesman and Girling (1990) which indicates how much theextinguishing water should be diluted to allow fish life to be sustained.

Further actionAll aspects of the involvement in the fire of MDI or TDI should be reviewedin detail, to understand what further precautions should be implemented.

On-going actionWhenever there are significant changes to plant processes or to site lay-out thefire safety implications should be reviewed.

Transport of MDI and TDI

MDI and TDI are routinely transported in large quantities by land, by sea andby air. Most is transported without a drop being spilled. This safe transportrequires active cooperation between all those involved in the transport anddistribution chain. Appropriate handling procedures must be established forthe wide variety of container sizes in use. Examples of these include:

• ships’ tanks, typically 1 000 000 litres;• rail tankers/ cargo tank trucks, typically 40 000 to 80 000 litres;• road tank containers, ISO containers and other transferable tanks, typically

20 000 litres;• intermediate bulk containers, typically 1 000 litres;


• cylinders, for example 200 and 870 litres;• metal and plastic drums, typically 200 litres;• metal cans, pails and totes of various sizes and designs.

1000 litres is equivalent to264 US gallons

Care must be exercised to avoid all contamination of the chemicals, particularlyby moisture, and to maintain specified temperatures. Preservation of productintegrity is important both for the manufacture of high quality polyurethanes,and for safe handling. Guidelines to establish appropriate high standards forthe distribution of MDI and TDI have been prepared (API, 2000a, 2000b;ISOPA, 2002).

Transport regulations

Examples of transport regulatory authoritiesand requirements are:

Air: ICAO International Civil AviationOrganization

Sea: IMO International MaritimeOrganization

Road: ADR Accord Europeen relatif autransport international desmarchandises dangereusespar route

Rail: RID Reglement internationalconcernant le transport desmarchandises dangereusespar chemin de fer

Con-tainer:

CSC International conventionfor safe containers

There are United Nations (UN) recommendations, whichare presented as Model regulations on the transport ofdangerous goods, addressed to governments and internationalorganizations, who apply them as a basis for nationaland international transport regulations. If particular nationalauthorities apply different requirements from those of theinternational organization, then the more stringent requirementshave to be followed. For example, the US Departmentof Transport requirements are more stringent than the UNrecommendations.

The criteria for transport classification are broadly basedon acute hazard and physicochemical properties. The UNrecommendations classify substances into nine classes as afunction of these inherent properties, and regulated substancesare given a UN Number. TDI has UN Number 2078; it is

classified as Toxic Class 6.1. For the transport of packaged TDI goods, UNPackaging Group II performance standards must be complied with. MDI hasbeen de-classified by the UN, and hence has no UN number. In the UnitedStates, a number of regulatory requirements must be met when transportingTDI by any means, and when transporting MDI in quantities greater than5000 lb.

It is accepted practice for those transporting diisocyanates by road to carrywritten instructions for an emergency situation. This can take the form of anemergency procedure guide, as given in Figure 2.15. In the United States thisincludes a shipping paper which must contain an emergency contact telephonenumber, and a statement that the material is shipped in compliance with theregulations and emergency response information.

In Europe there is a system of TREMCARDS (transport emergency cards)which applies to consignments of dangerous goods transported under the ADRand RID areas of influence. These cards also give information on propertiesof the chemical, and on the personal protection required in case of spillage, aswell as an emergency telephone number to be used in the case of incidents.Although MDI is no longer classified by the UN, it has become acceptedpractice in Europe for the producers to provide carriers with printed instructionsfor emergency situations.


Contents of a typical Emergency Transport Guide for a diisocyanate

Transport classification numbers

Name of substance

Description of substance (colour, freezing behaviour, water miscibility)

Nature of hazard (toxicity, irritancy, fire behaviour)

Protective equipment required (respiratory protection, goggles, clothing)

In the event of an emergency

Whom to notify

Actions to take if there is a spillage

Actions to take if there is a fire

First Aid procedures

Figure 2.15 Contents of a typical emergency transport guide for a diisocyanate

MDI and TDI: transport temperatures

To maintain product quality and for safety reasons, it is important that MDIand TDI are transported at suitable temperatures. There are several gradesof MDI and TDI, and many types of derived prepolymers and other partialreaction products. The supplier’s guidance should always be followed onsuitable transport temperatures for these products.

Where possible, suppliers deliver diisocyanates at temperatures appropriatefor their customers’ use. It is common practice for suppliers to chargepolymeric MDI and TDI into the tanks used for transport near the topof the recommended temperature range, to allow for some cooling duringtransport. Deliveries in bulk are often planned so that the customer receivesthe diisocyanate at the temperature preferred for handling and use. Tankerdeliveries of polymeric MDI are typically between 30 and 45 ◦C (86 and113 ◦F). The viscosity of polymeric MDI depends on the temperature andif the temperatures are too low it may be difficult to pump.

The quality of pure MDI will deteriorate quickly unless it is handledcorrectly. MDI dimer may form and result in turbidity or the precipitation ofdimer solids in the liquid. Pure MDI melts at 40 ◦C (104 ◦F). Suppliers deliver

See Part 2, The workplacebelow for more details.

pure MDI either in the frozen state, or as a liquid held between 40 and 45 ◦C(104 and 113 ◦F), to minimize dimer formation. The optimum temperature forstoring pure MDI over extended periods is below 0 ◦C (32 ◦F).

TDI is delivered in bulk at 20 to 30 ◦C (68 to 86 ◦F), and in drums withouttemperature control. It tends to crystallize out at temperatures below 15 ◦C(59 ◦F). If crystallization of 80/20 TDI occurs, it is important that it is wellmixed after thawing completely to ensure that the two isomeric forms aredistributed homogeneously. The recommended temperature range for handlingTDI in the workplace is greater than 15 ◦C (59 ◦F) and not above 30 ◦C (86 ◦F).


Typical containers for the transport of diisocyanatesRail tank cars, road tankers and inter-modal tank containersTanks and equipment can be constructed of mild steel (coated), butstainless steel is recommended for ease of cleaning and minimizing productdeterioration. Rail tank cars (Figure 2.16), road tankers (Figure 2.17) and inter-modal tank containers used for the transport of all chemicals must meet thedesign and construction requirements of the various national and internationalregulations. The regulations cover the requirements for aspects such asconstruction materials, welding, wall thickness, gaskets, valve protection andventing devices and should be consulted for detailed information.

Side view

Top view

ThermowellSafetyvalve

Topunloading

valve

Pressureconnection

Sample valve

Top unloading valve

Steamoutlet

Steaminlet

Safety platform

Figure 2.16 Typical tank car

It is recommended that product vapour return and dry gas pressureconnections on all tanks/vehicles should be clearly labelled. The labels shouldbe in the language(s) of the consignor and destination and in an internationallanguage, often English, on journeys through other countries.

Tanks should be thermally insulated to minimize deleterious temperaturedeviations. The insulation will provide extra protection in the event of an


Sample valve

Unloadingconnection Steam outlet

Airdrier

Loading line

Safety valve andpressure gauge

Dry air/nitrogenconnection

Vent line

Steam inlet

Figure 2.17 Typical tank truck

accident or fire in the vicinity. Heating coils should preferably be oil filled.They should be located on the exterior of the tank, and regulated to a maximumtemperature of 60 ◦C (140 ◦F).

Although some regulations permit bottom outlets, top outlets through a diptube may be preferred to prevent the possibility of leakage. Tanks should befitted with connections for vapour return lines, which are typically 2 inches inthe USA, and 50 mm in Europe. Pressure relief valves, protected by burstingdiscs, should be fitted. A pressure gauge should be fitted in the space betweenthe bursting discs and the relief valve. Vacuum relief valves should be presentto prevent negative internal pressure, for example a vacuum that developsduring unloading by pump. Fittings must be available for pressurizing the tankcar with dry air (dew point −40 ◦C, which is also −40 ◦F) or dry nitrogen toassist in unloading or to apply a blanket to prevent entry of moisture.

A rail tank car must have roll-over crash protection on external fittings sothat the rail tank car will not leak if involved in an accident. Thermowellsfor temperature-measuring devices should be fitted and have the appropriaterelief devices to prevent spraying of the product in the event of damage tothe thermowell. Emergency information panels (placards) should be locatedon both sides of the tank as well as at both ends, so that if the container islying on its side following an accident, then at least one label will be visible.Any opening which people are required to enter at any time must exceed aminimum diameter. The cover should have hinged swing bolts.

Intermediate bulk containersIntermediate bulk containers (IBCs) allow efficient transport and handling ofdiisocyanates in quantities convenient to many polyurethane manufacturers.The term IBC in Europe refers to a container of size 1000 litres, whereas inthe USA the term covers containers of a range of sizes between drums andbulk transport vessels. Some IBCs have casings which allow lifting by a forklift truck; other IBCs can be moved on pallets. IBCs with metal frames can


High densitypolyethyleneinner tank

Multi-wallcorrugatedouter shell

Dischargevalve

High densitypolyethylenetank

Tubularsteel grid

Dischargevalve

(b)

(c)

Protectivecap

Dischargevalve

Outlet fitting,male section

Desiccantcartridge

(a)

Figure 2.18 Some types of IBC. (a) Stainless steel IBC. Reproduced with permission from Guidelines for theDesign and the Handling of Stainless Steel IBCs for Diisocyanates and Components of Polyurethane Systems,ISOPA, 1996. (b) IBC with a polyethylene tank within a stainless steel grid (Schutz Container Systems, Inc.,1995). (c) IBC with a polyethylene tank within a multi-wall corrugated shell, Hoover Bulkdrum II (HooverMaterials Handling Group, Inc., 1996)

also be moved by rolling conveyors, and the containers can be stacked up tothree high when filled (Figure 2.18).

IBCs are available in different designs and materials. IBCs suitable foreither TDI or for polymeric MDI are made from stainless steel (ISOPA, 1996,1997b). IBC transport for TDI is restricted to the use of metal IBCs only. Metaland nondisposable polyethylene IBCs are refilled by the supplier. Some IBCsfor polymeric MDI consist of a disposable polyethylene container inside anouter casing. These containers are disposed of safely when empty by specialistcontractors.


Although MDI is no longer classified by the UN, it is generally agreedwithin the diisocyanate-producing industry that the packaging should meet therecommendations of UN Packaging Group III. IBCs are not recommendedfor the transportation of pure MDI because the containers are unheated andthe pure MDI would solidify due to its relatively high freezing point, 40 ◦C(104 ◦F).

An IBC should not be filled to more than 98 % of its capacity. The containerlifetime should be monitored and recorded by means of periodic inspections.Suppliers will be able to advise on the most suitable container for a particularuser situation.

DrumsThe material of the drum, including any fittings, should not cause productdeterioration. International modal regulations include a requirement for thedrums to bear a certification mark indicating compliance with the UNpackaging performance standards. In some countries regulations may differfrom these and must be consulted directly. There should be an inspectionregime immediately prior to drum filling. Drums must be undamaged, dry,clean and free of rust or other particulate matter.

Drums should be wire-banded or shrink-wrapped when transported on palletsto prevent movement. Drums of pure MDI should be transported in refrigeratedcontainers at −20 to 0 ◦C (−4 to 32 ◦F) to prevent dimerization of the MDI.Diisocyanate drums should not be transported on a truck with flammablematerials.

See Part 2, The workplace:storage and use of MDI andTDI for further information.

Pallets of drums, shrink-wrapped or banded, can be unloaded by a fork lifttruck. Individual drums can be unloaded using a fork lift truck fitted withspecial drum handling equipment. Drum clamps or grabs are suitable for somedesigns of drums, but may cause damage to others. The supplier should beconsulted if there is any doubt about the type of equipment best suited fora particular design of drum. Where fork lift trucks are not available, drumsmay have to be unloaded manually. Ideally, the drums should be carefullyrolled down an inclined plane. The dropping of drums from a truck shouldbe done only with extreme caution by rolling the drum from the tailboardand dropping it on to a drop cushion, a slab of high density foam or a bedof tyres. During unloading, drums should be inspected for damage and toensure that they are properly labelled. If damaged drums are identified, theyshould be examined carefully for splits, leaks or punctures. Leaking drumsshould be sealed if possible and removed to a dry, well-ventilated area andthe contents transferred to other suitable containers. Empty drums should bedecontaminated or sent to a specialist contractor. Bulging drums are evidenceof pressure build-up and they must be segregated with great caution, and dealtwith as described in Key Theme 6, Dealing with accidents.

Other containersVarious other containers are also used for the transport of polymeric MDI andof TDI. These include totes of various types and sizes, pails (small drums withtop handles) and pressurized carbon steel cylinders, ranging from a drum toa bulk container in capacity. In Japan, small containers such as 18 litre cans


are commonly used. Some types of containers are used by one supplier only,who should be consulted directly if specific questions arise about their use orsuitability for particular applications.

Responsibilities of carriersSafety auditing of drivers and vehicles deliveringbulk consignmentsOnly professional carriers, who understand the safety precautions thatmust be taken, should undertake transportation of MDI, TDI and modifieddiisocyanates. Regardless of the mode, i.e. land, rail, air, inland waterwayor sea, the carriers should demonstrate through policies, programmes andoperating practices that they have management commitment to safety andregulatory compliance. The carriers selected must exhibit their ability totransport all diisocyanate materials in a manner that assures the health andsafety of their employees, the end user, the communities through which theytravel, as well as the environment. It is important that manufacturers anddistributors develop safety review processes which measure the carriers’ safetyfitness and that feedback is provided to the carriers on any safety performance

Carrier safety auditprotocols have beendeveloped in the USA bythe American PlasticsCouncil and in Europe byConseil Europeen desFederations de l’IndustrieChimique (CEFIC).

deficiencies. This process should establish measures and goals that will leadto long-term safety improvements.

Contractual arrangements with carriers should state explicitly that thetransport must not be subcontracted without prior written approval of thesupplier. Thus, when multi-modal transport is used, the final carrier must not beregarded as the subcontractor; the MDI or TDI supplier should also control thatcarrier. The primary carrier should not change the secondary carrier withoutprior written approval of the supplier. Operating procedures at the dischargefacility should be the responsibility of the receiver (see below).

Product training for driversNational and international agreements require that drivers of road tankers (tanktrucks) or transport units carrying tanks over a defined capacity must havecompleted a training course on the particular requirements that have to be metduring the transport of dangerous goods. In addition, the hazards associatedwith MDI and TDI are such that drivers should be specifically trained eitherby the manufacturers or the carriers to understand the particular nature ofthe problems which may arise during the transport of these products and theactions to be taken in an emergency.

Therefore, before drivers are allowed to transport MDI and TDI, theyshould have:Transportation guidelines

API (2000a, 2000b);SPI (1996g); ISOPA (1992).

• received training to the standards required by the regulatory authorities in theareas in which they will operate. In the United States, a driver should have aCommercial Drivers License containing a Hazardous Materials endorsement.

• participated successfully in a specific training course for diisocyanates. Atraining package is available (ISOPA, 2000).

Before a manufacturer enlists a carrier he should ensure that the carrier can doc-ument that all drivers transporting MDI and TDI have been trained according


to the regulations. A supplier should include training as an item to be addressedin the carrier audit programme.

Pre-transfer inspectionWritten operating instructions covering the loading and unloading operationsof MDI or TDI should be available. Information and training regarding thespecific hazards of MDI and TDI must be given to all individuals involved inthe loading and unloading. Additionally, workers must be trained in the properprocedures for the operation of the loading and unloading equipment in bothnormal operations and in emergency situations.

Drivers must also be familiar with safety procedures and the use of safetyequipment at the loading and unloading points which should include a safetyshower and eye wash facilities. Appropriate personal protective equipmentmust be available for loading and unloading operations and workers must betrained in the correct use of this equipment.

Protective equipment for the transfer of MDI and TDI productsFor the transfer of MDI and TDI, personal protective equipment should beused. This will consist of:

• goggles;• safety helmet;• overalls (coveralls);• impervious gloves;• impervious boots.

For TDI, and where there is a possibility of inhalation of vapour of MDI,for example during sampling or the connection/disconnection of hose joints,suitable respiratory equipment should also be worn.

Self-contained breathing equipment should be provided ready for use at thetanker discharge points for use in case of a spillage or other emergency. Personsdealing with a spillage of TDI, or of MDI at elevated temperatures, should beprotected by impervious suits and must use respiratory protection in additionto the normal protective clothing described above (Figure 2.19).

See Key Theme 4: Usingpersonal protectiveequipment.

Distribution of MDI and TDI

Road transportThe carrier is responsible for the safe transport of MDI and TDI by road fromthe loading point to the unloading point and should plan a route that can begiven, on request, to the supplier. Compliance with bridge, tunnel or localrouting regulations or restrictions is entirely the responsibility of the carrier.As is usual with all chemicals, the route should follow major roads and avoidareas of high population density where possible.

Temperature checks of the tank contents should be made regularly andlogged. If the temperature of the tank contents should rise more than 5 ◦C(10 ◦F) above that specified by the supplier, the driver should immediately


Figure 2.19 Full protective equipment

telephone the supplier to seek instructions. Drivers should make checks duringthe course of transportation as follows:

• when there is a change of driver;• after the vehicle has been driven for 3 to 4 h, or after the vehicle has been

driven for 240 km (150 miles), whichever occurs first.

Safe parking is essential. Drivers of vehicles transporting MDI and TDI mustensure that the vehicle is either supervised at all times or is parked in a safeplace. A secure depot or secure factory premises should be used wheneverpossible. Preferably, parking should be in an isolated position in the open inan area that is lit at night. It is strongly recommended that receivers providesecure parking for vehicles that have arrived outside specific access times.

When severe weather conditions are experienced during the transport of MDIand TDI the vehicle must stop at the next suitable parking place. The vehicleshould not continue with the delivery until the weather conditions improve. Alldelays during transport, whether caused by severe weather conditions, break-down or any other reason, must be reported to the customer and/or supplier assoon as possible.

In the event of an accident during the journey involving the immobiliza-tion of the vehicle, product spillage, or a threatened loss of containment, the


procedure for obtaining emergency assistance as specified in the emergencyguidance procedures laid down by the suppliers should be followed. Details ofthe accident must be reported to the supplier and/or customer urgently.

Rail transportThe appropriate railway company or authority is responsible for the safe trans-port of the MDI and TDI by rail from the dispatch siding to the final receptionsiding. The selection of the route, intermediate stopping locations and cessa-tion of traffic due to severe weather conditions are matters to be decided bythe railway authorities, and should be reported to the supplier.

The railway companies will intervene in the event of an emergency involvinga rail car containing MDI or TDI. These companies should already have beenmade aware of product hazard information to aid railway hazardous cargointervention teams. It is recommended that rail tank cars should be labelled withthe supplier’s telephone number for use in an emergency. Railway companiesshould also be made aware of any available transport emergency scheme forproviding assistance at transport incidents.

Where road–rail–road movements are arranged which are not driver-accom-panied during the rail stage, particular attention must be given to ensuringthat the road vehicle performing the final delivery is accompanied by theappropriate emergency response information.

Transport by sea or inland waterMDI and TDI can be transported in:

• bulk ocean tankers or inland waterway vessels;• inter-modal tank containers that are lifted on and off container vessels;• inter-modal tank containers, with roll-on/roll-off chassis;• intermediate bulk containers (IBCs) which should be transported in

freight containers;• nonbulk packaging such as drums.

All relevant local, national, federal and international regulations such as theInternational Maritime Dangerous Goods Code must be observed.

Because of the nature of the activity, a number of different organizationsmay be involved in the operation of transporting MDI and TDI from supplier tocustomer. These may include the shipping company, port or harbour authoritiesand carriers. The supplier should consider carrying out a safety audit of thefollowing transport operations:

• the loading/unloading facilities at container terminals;• emergency handling within hazardous cargo yards at container terminals.

Unloading operationsCriteria for unloading facilitiesIt is important that unloading facilities are correctly designed and constructed.There should be an unrestricted escape route from the unloading site. Theoperation of unloading MDI or TDI from any road tanker, tank container, rail


tank car or small tank container is potentially hazardous. Both pressure orpump methods are used. There are differing views on the relative safety of thetwo methods. If pressure unloading is used, the displaced vapour cannot bereturned to the tanker, and has to be removed from the air before venting tothe atmosphere. If pump unloading is used, the vapour will be returned to thetanker and the potential releases to atmosphere will be negligible (there is stillsome venting via a scrubber or filter at the end of the operation). The equipmentshould be subject to regular reviews or audits to ensure the maintenance of therequired standards.

Criteria for hosesIt is strongly recommended that all hoses used for product unloading be ded-icated to MDI or TDI service and either be fitted with a ball valve at thetanker connection end or have an equivalent means of sealing the hose. Theunloading hoses for diisocyanates should preferably have different couplings(size and type) to prevent inadvertent connection to the wrong storage vessels.Colour coded hoses stamped ‘For diisocyanate use only’ are useful additionalsafety measures. Pressure testing is recommended prior to initial use, andquarterly thereafter.

Operating proceduresWritten operating procedures covering all aspects of the unloading of MDI andTDI must be prepared by the owner of the unloading facility and agreed withthe carrier, with the division of responsibilities clearly defined and followed.However, before the product is unloaded, the receiver should carry out checksto verify that the product complies with the documentation, and then certifyin writing that:

• the goods can be safely received at the storage location;• the hose is connected to the correct point.

The lines should be installed to the customer facility first, and the diisocyanatetank second. Connection and disconnection of the product lines should becarried out with great care, to prevent contamination of the diisocyanate. Atleast one person, driver or operator, should be present and watch the dischargeall the time (API, 2000a, 2000b). Nonessential personnel should leave thearea during discharge. Exclusion barriers should be provided to ensure thatnonessential personnel do not enter the area inadvertently during unloading.Product transfer can be monitored by means of flow meters or by loss in weightof the tank cars.

Protective equipment for operatorsAll necessary protective clothing and emergency equipment should be avail-able for unloading operations. Persons should be trained in the correct use ofthis clothing and equipment. Whenever the driver leaves his vehicle duringunloading, he should take with him his personal protective equipment to besure of its availability in the event of an emergency.


Inspection of the bulk storage facilitiesThe conditions for the storage of bulk deliveries of MDI and TDI at a cus-tomer’s premises are the customer’s responsibility. It is recommended thatsuppliers, in cooperation with customers, should arrange an inspection of thebulk reception facilities prior to an initial delivery and at agreed intervals.The objective is to ensure that good safety standards pertain during producthandling and storage. The site for the location of storage vessels should becarefully chosen. It is particularly important that the discharge site be con-structed so that any spillage is contained and is not able to enter surface wateror drainage systems.

See Part 2, The workplace:storage and use of MDI andTDI for further details.

Check list of equipment guidelines and requirements for tanktruck deliveriesManufacturers of MDI and TDI may provide their customers with a check listrelevant to their particular situation to ensure that the most important safetyrequirements during unloading of the diisocyanates are considered. The fol-lowing is an example.

EQUIPMENT GUIDELINES AND REQUIREMENTS FOR TANKTRUCK DELIVERIESTank truck unloading area

√Suitable location of unloading site√Safe access/egress for tractor, trailer, driver and unloading operator

• Impervious spill containment• Unimpeded access to a safety shower and eyewash• Fire extinguisher (as per specific MSDS)√

Wheel chocks utilized• Communications access (radio, telephone)√

Access to spill cleanup materials (as per specific MSDS)√Written unloading procedures√Trained personnel–product, equipment, process and procedures√DOT training requirement met (49 CFR 172.700–704)√Appropriate personal protective equipment utilized (as per specific

MSDS)√All fittings, piping, valves and tanks clearly identified√Vapor return or proper treatment of vapors from storage tank√Piping material of construction to be carbon steel or stainless steel

• Flanged, welded pipe connections√Piping traced, insulated and jacketed as necessary for temperature

control• Male Kamlok type fitting on customer piping for unloading hose

connection√Isolation valve as close as possible to unloading hose connection

• Check valve on storage tank side of unloading hose connection• Drain/vent valve between isolation valve and unloading hose

connection√Fittings and drain valves capped or plugged when not in use

• Carrier-supplied hoses utilized for product transfer and vapor return


• 2 inch piping and hoses for isocyanates• 2 inch hose and fittings for vapor return• 1 1

2 inch diameter piping minimum for vapour return• Isolation valve as close as possible to vapour hose connection

Pump unloading

√Customer-supplied unloading pump

• Sealless pump• Pumps, strainers and filters inside secondary containment• Strainer on suction side of pump√

Piping system and equipment drain valves to be capped or pluggedwhen not in use

• Pressure gauge on discharge side of pump and on suction/dischargesides of filters

• Bypass around unloading pump (may require proper treatment ofvapours)√

Vapour return to tank truck or proper treatment of vapours fromstorage tank

• Pressure vacuum combination gauge on vapour return piping

Pressure unloading

√Nitrogen or dry air source with −40 ◦F dew point

• Pressure gauge on unloading piping√Proper treatment of vapours from storage tank

√Supplier requirement • Best industry practice

This information is taken, with permission, from the 2001 product stewardship literature of Bayer

Corporation, USA.

Accidents and emergenciesEmergency proceduresAll persons dealing with emergencies involving MDI or TDI should wear fullemergency equipment; the use of self-contained breathing apparatus is essen-tial. See Key Theme 4: Using personal protective equipment. If a diisocyanateleak or spill occurs during transport, the diisocyanate should be contained asmuch as possible by the use of wet earth or wet sand where local conditionsallow it. See Key Theme 6: Dealing with accidents. In all cases of large spillsor leaks the supplier of the diisocyanate should be contacted without delay foradvice and help relevant to the specific situation. Small spills or leaks should betreated with an absorbent material and neutralized and the residues disposed ofsafely in accordance with local regulations. See Key Theme 3: Neutralization,decontamination and disposal of wastes.

MDI and TDI do not ignite easily, but in a fire will burn and give offcombustion gases typical of any organic material containing nitrogen. SeePart 5.5. Fire behaviour of MDI and TDI.


Schemes for providing assistance at transport/unloadingemergenciesNational emergency response schemes exist in various countries throughoutthe world. All responsible chemical companies involved in the transport ofMDI and TDI should ensure that there is a means of receiving transport emer-gency messages (24 h manning) and for providing expert advice to minimizeany hazard arising from an incident on road, rail or water. Additionally, theymay attend the scene of the incident, or may take or assist in remedial actionto resolve the problem. In cases where the local or national emergency author-ities are in control of the incident, the role of the company representativeswould be:

• to offer advice based on technical product knowledge;• when requested by and agreed with the emergency authorities, to organize

the provision of spare vehicles/pumps/hoses/other equipment, cargo transferand decontamination;

• to be prepared on behalf of the emergency authorities to employ their tech-nical expertise in the conduct and supervision of remedial action to renderthe incident safe.

Because of the large geographical areas involved in the transport of MDI andTDI, the ability of an individual chemical company to provide expert advicequickly at the scene of an incident may be severely restricted due to thedistance involved. However, a contact point for technical information shouldalways be available.

The workplace: storage and use of MDI and TDI

MDI and TDI are very widely used in many locations for manufacturing

Additional information willbe found in the precedingKey Themes.

polyurethanes. These range from small operations with a few drums of diiso-cyanate stock to very large production units with fully automated systems, andbulk storage in tank farms. However, there are common approaches to protect-ing the workforce, and common requirements for preserving product integritythat may have a bearing on safety. There are also requirements to minimizereleases and to dispose of waste materials safely, so that local communitiesand the environment are not adversely affected.

Once MDI or TDI has been accepted into storage (see Part 2, Transportof MDI and TDI ) the responsibility for its safe handling and use rests withthe site management. Supervisors need to ensure that the responsibilities forsafety are well defined, understood and adhered to. Provision of suitabletraining and retraining on all aspects of the safe handling of MDI and TDIform an important part of ensuring that safe working practices are applied,whether during normal operations or in the case of emergencies. Routinemedical surveillance for those potentially exposed to diisocyanates shouldbe provided. Visitors to all chemical sites need special consideration, asthey may be unaware of the necessary precautions where diisocyanates arebeing handled.

See Key Theme 2:Protecting health.


Designing the systems and minimizing the risks

An integrated approach to workplace risk management has to start with therecognition that there will be no single solution for all situations. Each typeof process, automated or manual, and each storage facility will require itsown control systems, maintenance schedules and training procedures. Caremust be taken to ensure that these comply with regulations and local prac-tices. The engineering control of MDI and TDI exposure will generally fallinto two categories: physical barriers to minimize releases of diisocyanate intothe workplace and exhaust ventilation. Whilst control measures by engineer-ing means are always preferred to personal protection, the normal personalprotective equipment for chemical environments will always be required.

The first step in designing the systems and minimizing the risks is to assessthe ways in which people can be exposed to the materials used. Since releasescan be airborne (vapour, spray, aerosols or dust), solid or liquid, exposurecan be either by inhalation or by skin contact. It is difficult to predict whichcontrol strategies will be required for a particular process without actuallymeasuring the releases from that process under normal working conditions. Ingeneral, the inhalation risks are greatest where the process involves spraying,or heating in the absence of adequate ventilation. Particular problems may ariseduring maintenance when work may need to be carried out in confined andunventilated spaces.

MDI and modified MDIs are of very low volatility, and present very littlevapour risk unless heated or sprayed, though solid MDI in the form of flake canpresent a risk if the dust is inhaled. MDI may be released from rising foam,especially near filling holes or air vents in large closed moulds. Althoughthe concentrations may be low and of brief duration, the need for ventila-tion at these points may need to be considered. Aerosols are produced duringbonding processes which use sprayed MDI adhesives or during spray foaminsulation work. Air-supplied respiratory protection is essential for manual dis-pensing or spraying of MDI-based foams and adhesives, unless measurementsdemonstrate that engineering control is sufficient to reduce the concentrationof MDI to below the Occupational Exposure Limit (OEL). Manual dispensingof one-component foam does not normally require such protection. Spraying ofreaction mixtures outdoors always requires air-supplied respiratory protectionsince engineering control is not possible.

TDI is much more volatile than MDI. Exhaust ventilation is usually essentialin the processing of TDI-based polyurethanes, whereas it may not always beneeded for the processing of MDI. It should be recognized that there areother chemicals used in the manufacture of polyurethanes and these may alsopresent hazards associated with toxicity or environmental impact. These needto be investigated in their own right.

Processing equipment should be designed with the demands of the user inmind, to make it simple to use, clean and maintain. Whenever possible, controlof releases into the workplace should be part of the design, especially as thereis increasing pressure to minimize releases and waste, and as the costs of thetreatment of releases and waste disposal rise ever higher. Improvement in thedesign of existing plant is often economically justifiable when compared to thecosts of bolt-on remediation or down-stream charges for waste handling.


A process that requires the operator to wear respiratory protective equip-ment and impermeable clothing continuously as a necessary precaution is tobe avoided. Personal protective equipment will, however, still be needed forvarious reasons discussed below. Careful examination of a block diagram ofthe plant or process can yield foreseeable points of releases. A critical analysisof these areas will provide solutions to eliminate or minimize the release.

Assessment of workplace exposureEvery safety scheme will need to incorporate an assessment of the potentialexposure of the workforce. This assessment is central to risk management. Thematerials processed and the process equipment all need to be included in theassessment. The different jobs in the workplace where diisocyanate exposuremay possibly occur, including maintenance, repair and cleaning tasks, must alsobe assessed. The assessment may well be rather complex; its conclusions willthen need to be simplified into action plans and instructions. The assessmentwill be iterative. A quick review may reduce the safety options from manyto a few. A more detailed review leaves two or three preferred options. Eachthen needs a thorough design costing and review before a final choice ofcontrol measures is made. The assessment may conclude that different levelsof personal protection are required for different jobs.

Raw materialsEven before chemicals are delivered, the supplier should provide compre-hensive safety information about them such as product data sheets. Mostmanufacturers of MDI and TDI subscribe to schemes of Product Steward-ship under which they commit to provide information and advice on theirproducts. When products are purchased from merchants or secondary suppli-ers, and not direct from primary manufacturers, the information may be lesscomplete. Even when labels, or documents such as material safety data sheetsgiving all the basic information, are made available there may be unresolvedquestions on safety. Those handling diisocyanates should make every effort toobtain help from their suppliers to resolve safety problems.

Engineering control considerationsIn many countries, legislation is moving away from specific items on a check-list towards compliance with principles. The extent of this change varies fromcountry to country. In the European Union, for example, quite general essen-tial health and safety requirements are set down, applicable to all types ofmachinery and processes.

When new machinery is to be purchased, the following points should bediscussed with the suppliers of the machine and of the chemicals that are tobe used:

• equipment scope and limitations;• materials consumed and produced;• types of potential releases;• extent and location of possible releases;• control measures needed;


• constraints on implementation of preferred control measures;• training, maintenance and supervision needed;• running and waste disposal cost implications of the process.

Many of the points above are equally relevant to assessments of existingmachinery.

The quality of safety information provided with plant and equipment variesgreatly. For example, the European Union requirements apply only to newmachinery. If the process machinery is put together by the purchaser fromnonspecific components (drives, valves, etc.) and from local fabrications, therewill be little or no health risk control information available from componentsuppliers and the safety assessment process is then essential.

Strategy for monitoring workplace releasesStringent workplace exposure limits for diisocyanates have been set world-wide. Moreover, in many countries MDI and TDI have been categorized amongsubstances for which the exposure should be reduced as far below the occupa-tional exposure limit as is reasonable: consequently, measurement of workplaceexposure levels will always be necessary as part of a baseline assessment. Allpossible sources of releases should be dealt with, even if personal exposuresare already below the limit.

Monitoring of workplace exposure provides data to:

• verify compliance with regulatory exposure limits.• estimate exposures of individuals to diisocyanates. Such estimates can be

associated with health measurements (see Key Theme 2).• assist in checking the effectiveness of the engineering control measures. This

exercise should be accompanied by tests on equipment and factory systems,and logged, so that causes of high exposure can be determined.

• confirm or extend the assessment of the workplace and direct attention tosources of releases that may have been overlooked. It is necessary to con-sider any anomalies in the results of monitoring, and to look for trendsand associations, not merely to record the data as being above or belowthe limit.

The design of a monitoring strategy will be influenced by the types of engi-neering control, the polyurethane manufacturing process whether continuous ordiscontinuous, the diisocyanate, and the range of jobs. A person whose job isexclusively in a workplace containing a well-enclosed, well-ventilated processwill be able to rely on the principle ‘if it isn’t getting out of the process, it isn’tgetting to me’; and personal monitoring can be reduced in scale and frequencyin favour of continuous monitoring close to possible points of emission fromthe process. However, a person such as a maintenance operator, whose jobinvolves variable work in less predictable conditions, will need better assess-ment of all the tasks undertaken and may need to wear a personal monitorwhilst this is being carried out.

Long-term exposure monitoring results may be presented as an average (8 htime-weighted average) and/or detailed continuous record, depending upon theequipment. An average value may mask exposure peaks which are so high that


they might have a significant effect on respiratory health: this might happeneven though the average conforms to the required long-term limit. Averagesalone should be used only when there is considerable confidence that thereare no high excursions. Personal exposure records need to be linked to theworkplace assessment and the results from relevant fixed monitors capable ofdisclosing excursions.

To develop a monitoring strategy, various stages of data gathering andinformation collating must be carried out. Initially, an intensive basic sur-vey provides quantitative information on the exposure profile of each worker.This should include those routinely in the workplace, as well as people whoare occasionally or intermittently exposed such as cleaners and maintenancepersonnel. The data are acquired using personal and area monitors coveringall periods of significant exposure. There needs to be careful selection of boththe sampling techniques and the analytical methods to ensure that they aresuitable for the expected emissions. Process activities and any change in cir-cumstances during the sampling period should be logged. Figure 2.20 showsa typical personal monitoring unit being worn by a worker.

Figure 2.20 Worker wearing a personal monitoring unit (figure reproduced bycourtesy of Huntsman Polyurethanes)

A second and more detailed survey should be carried out if the intensivebasic survey reveals exposure levels above, or close to, the limits. This mayinvolve more detailed personal sampling (over shorter time periods) to identifyhigh excursions and, more commonly, a greater use of area samplers to pinpointthe problem sources. Sampling may be needed from several operations in eachwork area and for each shift to ensure that representative data are available. On


some occasions there may need to be measurements that distinguish betweenthe activities of individual employees, nominally doing the same job, sincework practices may be the source of over-exposure. Once the conclusions havebeen drawn from the basic and/or detailed survey, and remedial changes havealso been tested, the monitoring regime can revert to a routine programme.

Monitoring of a particular job exposure should be repeated monthly, oreven more frequently. This should continue until two consecutive determina-tions, at least 1 week apart, indicate that the exposure no longer approachesor exceeds the recommended occupational exposure limits. Suitable equip-ment for monitoring workplace exposure is described in Part 5.7, Samplingand analysis.

The nature and frequency of routine monitoring depends on the nature ofthe activity, as discussed above, and should be associated with a record ofengineering controls and operating circumstances at the time. For routine oper-ations with well-controlled processes, personal monitoring may be infrequent(e.g. annually), provided that it is combined with audible or visual alarmslinked to area monitors. For nonroutine or occasional operations, personal mon-itoring should be frequent enough to reveal variations, and should be combinedwith retraining and supervision of procedures when required. Monitoring andother pertinent records should be kept for at least 40 years after the employee’slast occupational exposure to diisocyanates, or as required by local regulations(NIOSH, 1978; HSE, 1997b).

Further basic or detailed surveys are indicated (unless a good exposureassessment concludes they are not needed) when

• a new process is started up;• there has been a significant change of equipment or materials in an exist-

ing process;• there has been a change in the occupational exposure limit;• there has been a substantial change in the rate, scale, staffing or procedures

of an existing activity;• abnormal, infrequent or special activities are to be carried out (for example,

decommissioning, major overhaul);• there are symptoms (for example, running nose or wheezing) suggesting that

there is some unidentified exposure among the workers.

In practice, there are differences between individuals and between shiftsgiving some random variation of monitoring results. However, the resultsshould be checked regularly for systematic variation which could indicatethe following:

• an individual’s poor working practices;• noncompliance with standard procedures;• poor supervision;• significant work load fluctuations.

Such findings should be translated into remedial actions, such as retrainingor better management control. In order to get the best value out of monitor-ing, it needs to be systematic and should include all stages of activities andtimes of a working day over a period of time. The discovery of high expo-sures or significant rising trends should result in an investigation and remedial


action. Depending upon the seriousness of the findings important questionsmight include:

• Is immediate action needed to reduce exposure (for example better personalprotection as a short-term measure)?

• Is action needed to control the source of the releases (for example by stop-ping the process)?

• Is a programme of planned improvements appropriate?• Is the cause unclear, so that more investigation and a detailed survey

are needed?• Should routine monitoring be intensified or extended?

Tables 2.6 and 2.7 give an indication of typical exposure levels to MDIand to TDI. The data in these tables summarize industrial hygiene informationcollected over many operational sites over several years. The concentrationsfound depend upon the actual operational conditions at the time the obser-vations were made, but indicate that broadly accepted occupational exposurelimits were complied with (see Key Theme 1: Know your product). However,such figures cannot be used to predict concentrations in other workplaces.Detailed measurements will always need to be carried out. Table 2.6 sum-marizes data collected from a wide range of applications and processes withinEurope over the period 1993 to 1998 (Dobbs, 1998, personal communication).Various standard sampling methods were used to capture total inhalable MDI(vapour and aerosol). Both personal and fixed position (area) monitors wereused. Table 2.7 summarizes data obtained during a comprehensive survey ofthe UK flexible foam industry over the period 1979 to 1986 (Clark et al.,1998; Bugler, 1999, personal communication). All TDI measurements weremade using continuous paper tape monitors worn on the chests of workersduring their normal work shifts.

Table 2.6 Typical workplace concentrations of MDI.

Application Sampling Number ofsamples

Concentrationof MDImg/m3

Lamination of rigid foam Area 89 <0.0019Insulation of refrigerators, freezers

and boilersArea and

personal50 0.0001 to 0.005

Spraying roofing insulation Area andpersonal

15 >0.05

In situ packaging foam Personal 34 <0.01 to 0.041Spraying waterproof primer coating Area 46 0.0001 to 0.008Oriented strand board: MDI used as

binderPersonal 48 <0.0001 to 0.021

Particle board: MDI used as binder Area 140 0.0001 to 0.05Thermoplastic elastomers: sprayed

MDIPersonal 50 <0.0001 to 0.0083

Typical values for occupational exposure limits are: Short-term (15 min): MDI 0.2 mg/m3. Long-term (8 h): MDI 0.05 mg/m3.


Table 2.7 Typical workplace concentrations of TDI in the UK flexible foam industry.

Activity Number ofpersonal

samples taken

Number offactoriessurveyed

Concentration of TDI(8 h time-weighted

average)mg/m3

MouldingHot cure: at pouring head 98 4 0.007 to 0.028Hot cure: demoulding, and

waxing of moulds75 4 0.005 to 0.006

Cold cure: pouring,demoulding, etc. Someformulations were based onMDI + TDI

113 6 <0.004 to 0.015

Cold cure: demoulding only 80 5 0.006 to 0.0086

Block foam manufactureAt dispensing head 141 9 0.008 to 0.019At paper take-off. Respiratory

protection often worn198a 9 0.017 to 0.047

Moving hot blocks 282 8 0.0065 to 0.025

aPredominantly area samples. Workers at paper take-off usually wore respiratory protection.Typical values for occupational exposure limits are: Short-term (15 min): TDI 0.14 mg/m3. Long-term (8 h): TDI0.036 mg/m3.

Physical and chemical properties relating to storageand processing

The physical and chemical properties of MDI and TDI impose constraintson the conditions under which they are stored and used in the workplace.Some relevant information is given in Key Theme 1: Know your productand further details are given in Parts 5, 5.3 and 5.4. Failure to handle andstore MDI and TDI under suitable conditions may give rise to risk and becostly. It is essential that MDI and TDI do not become contaminated prior touse. Scrupulous cleanliness of systems is essential for safe and economicallyviable operations. It is important that even waste diisocyanates are not mixedwith certain contaminants, as this can lead to the development of pressurein closed containers and lines. Overheating may cause the formation of harddeposits which could block pumps and lines, with significant losses of the finalpolyurethane product.

Water either as liquid or as vapour must be rigorously excluded from allproducts containing free MDI or TDI. The isocyanate groups react with watergiving insoluble polyureas with the liberation of carbon dioxide gas. Thisreaction is slow at workplace temperatures and in the absence of catalysts,but can be vigorous at elevated temperatures. Polyurea formation may causea build up or blockage especially in vents, valves or mixing heads. In closedcontainers or in restricted lines contamination by water as liquid may pro-duce carbon dioxide in sufficient quantities to cause rupture. Closed drumscan rupture with sufficient force to project them considerable distances. Anyevidence of carbon dioxide build up, such as a bulging drum, should be treated


as a potentially serious accident requiring immediate remedial action (seeKey Theme 6: Dealing with accidents for information on dealing with theseoccurrences).

Even small amounts of water can cause major problems. When reactedwith diisocyanate, 30 ml (about 1 fl oz) of water can release as much as40 litres (1.5 ft3) of carbon dioxide at normal temperature and pressure.In a 208 litre (55 gal) drum, 95 % full, this could result in a pressure of2 to 3 bar (approximately 30 to 40 psi), which would probably causethe drum to rupture.

MDI and TDI also react with manycommon materials, such as alcohols,ammonia, and acids, sometimes withgreat vigour and with the liberationof heat. Strong bases such as sodiumor potassium hydroxides catalyse therapid dimerization or trimerizationreactions producing solid deposits,

possibly with the liberation of carbon dioxide, both of which are undesirable.Further information is given in Part 5.3, Chemical reactions of MDI and TDI.Industrial cleaning agents containing sodium or potassium hydroxide mustnever be used for cleaning lines or vessels. Copper, zinc or their alloys suchas brass or bronze, which may be used in pipework or plant fittings, can formreaction products that may lead to product deterioration. Fittings and pipeworkare now often coated with PTFE to minimize contamination problems. Furtheradvice should be obtained from the equipment manufacturers.

0 10 20 30 40 50 60

Temperature (°C)

0

200

400

600

800

1000

1200

1400

Vis

cosi

ty (

mP

a s)

Figure 2.21 Polymeric MDI: temperature–viscosity profile

Figures 2.21 and 2.22 illustrate the changes in viscosity of polymeric MDIand TDI with temperature. Polymeric MDI becomes increasingly viscous withdecreasing temperatures and may become difficult to pump. Pure MDI meltsat 40 ◦C (104 ◦F) and is therefore a solid at normal workplace temperatures.


10 20 30

Temperature (°C)

2.0

2.5

3.0

3.5

4.0

4.5

Vis

cosi

ty (

mP

a s)

Figure 2.22 80/20 TDI: temperature–viscosity profile

Storage of MDI and TDIDeliveries of MDI or TDI to a customer will be either as bulk delivery inroad tank containers, in rail tankers, in ships’ tanks, in various types of bulkcontainers of intermediate size, or in metal drums, pails or cans of varioussizes. Ideally, the bulk storage facilities, which should be sited close to, butseparated from, the polyurethane user plants, must be capable of maintainingproduct integrity and have suitable provisions for the control of accidentalreleases. Whilst neither MDI nor TDI are easily ignited, both diisocyanatesshould be stored separately from combustible materials so that they will beprotected in the event of a fire.

In some countries there are regulations covering the storage of MDI andTDI in quantities above defined limits. As these may vary from time to time,companies must check those that apply to a particular storage facility.

Relevant regulations

The European Council Directive on the control of major accidenthazards involving dangerous substances and preparations applies tothe presence on a site of 10 tonnes or more of TDI. The Directiverequires safety plans and reports, and consideration of environmentalimpact. The Directive does not cover MDI.

The USEPA Risk Management Program, the purpose of whichis to prevent accidental releases of toxic, flammable or explosivesubstances, covers the storage of TDI, but not MDI. The EmergencyPlanning Community Right to Know Act (EPCRA) legislation, whichvaries by state, requires an inventory of all materials stored on site inexcess of defined amounts to be made available to the local emergencyplanning committee and to the community.

The relevant material safety data sheetsshould be available prior to the firstdelivery. The first step in acceptingany delivery of diisocyanate intostorage must be to confirm that thematerial delivered is that expected, byensuring that it is properly labelledand identified. The personnel involvedin transferring the material to storageshould be wearing the correct personalprotective equipment and should betrained in the operations to be carriedout. A ready-for-action, self-containedbreathing apparatus should be provided


at bulk delivery points for use in case of spillage or other emergency wheneither MDI or TDI is being discharged. Persons dealing with a spillageof MDI or TDI should also be protected by impervious suits. Appropriatedecontamination and other equipment should be readily available to deal withany spillage. Access to an emergency shower and eye wash equipment is alsoessential. When tank truck deliveries are being made, the driver needs to betold the location of the emergency equipment, which should be tested beforeunloading starts.

Storage in bulkUsers of large quantities of MDI and TDI will probably have the diisocyanatesdelivered in bulk in a road tanker, a demountable tank, a rail tank car orby ship tank (see Part 2, Transport of MDI and TDI ). Diisocyanate suppliedin this way will be transferred to dedicated bulk storage vessels. It is goodindustry practice that the storage vessels should be:

• reached by good roads, allowing easy access to delivery vehicles;• as close as possible to the using plant;• sited on stable ground;• sited away from any fire hazard;• sited separately from polyol tanks;• within a bunded (diked) area that will contain the contents if there is a

major leak. The containment area should, as a minimum, be able to containat least 110 % of the total contents of the largest tank within the confinementarea. The area should have an impervious surface. Concrete coated with animpervious material should be used; asphalt is not suitable, as it is oftenporous and the diisocyanate may soften the material. The system should bedesigned so that any leakage will be contained within the area, and will notenter the surface water or sewage drainage systems. Local regulations maydetermine the construction details of the containment facility.

Installations are usually designed to meet the particular requirements of acustomer. The detailed designs and choices of gauges, pumps, pipes and reliefvalves require specialist knowledge and experience. The diisocyanate suppliersshould be consulted for further details. Figure 2.23 illustrates a layout for atypical diisocyanate storage area.

There should be access to certified tank scales at the site or at anothersuitable location. Storage vessels should have a minimum capacity to acceptthe total contents of the delivery vehicle. This will reduce the potential forproblems arising from multiple connections. The tanks should be above groundand should be constructed of steel of a grade and type, lined or unlined,which is suitable for the product application. Carbon steel is often suitablefor polymeric MDI and for TDI. Stainless steel is preferred for applicationswhere colour variation in the final product must be avoided. The tanks shouldhave certification to allow them to accept positive pressure during pressureunloading or in the event of accidental product contamination. It is better ifstorage tanks can be located indoors, but if they have to be sited outside andexposed to extremes of temperature they should be insulated. Tank heatingjackets or exterior mounted coils may be used for heating where necessary,


Tank caror

tanktruck

Unloading& transfer pump

Heating medium

Storage tank

Level indicator

alarm

Safety ventvalve

Filter

Nitrogen blanketing system

To vent system/scrubber To process

Pressure control valve

Pressuregauge

Dialthermometer

Pressure gauge

Pressuregauge

Pressure control valve

Temperaturecontrol valve

Figure 2.23 Typical diisocyanate bulk storage system

and the design must include a top mounted agitator or other means of pre-venting local over-heating. Heat exchangers may also be used. They shouldpreferably be electrical or circulating hot oil yielding a maximum temperatureof 70 ◦C (158 ◦F). Steam heating is not recommended as it may overheat thediisocyanates. Typical storage temperatures for MDI and for TDI are given inTable 2.8.

Table 2.8 Typical storage temperatures for MDIand TDI.

Typical storage temperatures

◦C ◦F

Pure MDIas liquid 40 to 45 104 to 113as solid −20 to 0 −4 to 32

Polymeric MDI 15 to 25 59 to 77TDI 15 to 25 59 to 77

Polymeric MDI should not be held at 70 ◦C (158 ◦F) for more than 4 h. It isbeneficial to have provision to circulate the diisocyanate to achieve a uniformproduct temperature. It is recommended that tanks be equipped with tempera-ture monitoring systems that record the actual temperature of the product in thetanks. Skin thermometers are not recommended as they do not accurately mea-sure the product temperatures. Temperature alarms with high and low warningsare recommended. Monitoring is required to detect high temperature excursionswhich are typical of diisocyanate contamination with water. Additionally, it isimportant to control the temperature of the isocyanate because processes aresensitive to product temperature excursions, which in turn could give rise to


safety problems. The high temperature alarm should be set above the recom-mended storage temperature by 10 ◦C (18 ◦F) for polymeric MDI or TDI, andabove the maximum recommended temperature for pure MDI by 6 ◦C (11 ◦F).If the tanks are located indoors, and if sufficiently high ambient temperaturescan be maintained, jacketing may not be required for polymeric MDI and TDI.

MDI and TDI in storage tanks may be blanketed with dry air or nitrogen.Carbon dioxide alone is not recommended because of its solubility in MDIand TDI. Whichever blanketing gas is used, the water content should not begreater than 65 ppm (dew point of −40 ◦C, which is also −40 ◦F). This levelcan easily be achieved with both nitrogen and factory air dried by use of anin-line desiccant. Air entering a storage tank should be at working temperature.If it is hot it may purge the moisture from the desiccant and transfer it to thediisocyanate. This may be a problem when air from a compressor is used.Instrumentation for detecting the failure of the drying equipment for the purgegas is recommended. Compressor air must be oil free.

Lines leading to and from a storage tank should be constructed of similarmaterials to those of the storage tank and should be capped tightly immediatelyafter use. This will prevent moisture from coming into contact with residualdiisocyanate in the lines. Gaskets used in the transfer from a tanker shouldbe replaced each time a transfer is made. All pipework should be insulatedand traced where appropriate. Marking of MDI and TDI tanks, piping andconnections should be clearly identifiable. The pipe joints must not be threaded,but welded or flanged. Flexible hoses are required to make connections to thetanks. Hoses made from braided stainless steel lined with nitrile rubber orfluoroelastomers are suitable for low or medium pressure duty.

Storage tanks should be fitted with devices to prevent over-filling. Thesedevices detect the level of the contents and provide an audible and/or visualwarning when a predetermined level has been reached. The system then shutsthe inlet valve and prevents further ingress of material. An alarm to indicatelow levels should also be fitted. Sight glasses should not be used as the onlyindicator of liquid levels. If they are installed they must be protected againstaccidental breakage and installed in a manner not to permit complete drainageof the tank should they become damaged. Electronic devices are more suitable.

Diisocyanate may be transferred from the storage tanks by pumps. Thepumps should be immersed (for example in liquid paraffin) or canned. Seal-lesscanned pumps are recommended due to their ability to contain the material dur-ing pumping without leakage. While magnetic drive pumps are more expensive,their service-free extended life makes them more desirable for diisocyanate use.Strainers should be installed on the suction side of the pump to prevent dam-age to the impellers from foreign bodies or solids. Pressure gauges should beinstalled on the discharge side of the pump. All drain valves installed shouldremain plugged or capped when not in use. The pumps should be installedwithin the bund area and elevated for access at all times.

Filters should also be installed down stream from the pump and located inthe containment area. The filters should be elevated to promote ease of drainingand depressurization before opening. Drain and vent valves should be placedon the filter housing and equipped with caps/plugs. Pressure gauges installedon both the input and output side of the filter allow partial or total blockagesto be detected.


Tanks must have vacuum valves that allow the ingress of nitrogen or driedair when the liquid level falls. These provide excellent protection against tanksimploding during product transfer. It is essential that all tanks have someventing arrangements to allow small changes in pressure to be normalized,with the vent outlet fitted with a carbon cartridge to adsorb MDI or TDI fromthe released air. Emergency relief venting of diisocyanate storage tanks alsoneeds to be considered, given that activation of the system should occur onlyin most unusual circumstances. Worst-case scenarios should set the designrequirements. Relief valves contain the diisocyanate once the design pressureis established in the tank. However, because atmospheric moisture may reactwith diisocyanates in a relief valve to form solid polyureas and so jam thevalve, rupture discs should also be fitted at the outlet and the inlet of thevalve. At the inlet, the disc material should be as specified for use with thediisocyanate and the setting should be close to that of the relief valve itself.At the discharge side, the disc should be set at a very low pressure. Additionalemergency venting can be accomplished by the installation of a valved ventline. Regular inspections should be made of the tank and the relief valve/rupturedisc arrangements. A pressure sensor and indicator should be located betweenthe tank-side disc and the relief valve.

Transfers from storage tanks will necessitate the breaking of lines from timeto time, with the need to contain the contents safely. Personnel involved inthis work must wear protective clothing and have neutralizing materials readilyavailable. Where lines are disconnected and reconnected it is very importantthat safety devices are installed to prevent inadvertent reconnection of thewrong lines. The consequences of accidentally cross-loading diisocyanate intoa polyol tank, or vice versa, can be extremely severe and can cause a majorincident. The most effective way of preventing incorrect discharge is to usedifferent couplings (size and type) which are labelled to indicate the diiso-cyanate and polyol lines. However, it should not be assumed that the useof different couplings is a foolproof way of preventing cross-loading. Therehave been numerous cases where workers, convinced that they were actingcorrectly, have modified fittings, which allowed cross-loading. Colour-codedhoses and tagging with appropriate labels are useful additional safety measures.It is essential that the physical safety devices are accompanied by staff trainingand rigorous operating procedures to prevent cross-loading.

Pure MDI is transported in bulk in the molten state and must be maintainedbetween 40 and 45 ◦C (104 and 113 ◦F) at all times to minimize dimerization.If, on arrival, the temperature of the material in the tanks has fallen slightlybelow the recommended temperature, the heating system of the tanker shouldbe used until the correct temperature has been reached. The temperature mustbe monitored carefully to ensure that it does not exceed 48 ◦C (118 ◦F). Ifthe temperature has fallen well below the minimum temperature the suppliershould be contacted for advice.

Dimerization can be a safety issue since formation of solid dimer can causeproblems such as blockages. This reaction is temperature dependent and therate of formation of the white insoluble dimer is minimized between 40 and45 ◦C (104 and 113 ◦F) in the liquid state and below −10 ◦C (14 ◦F) in thesolid state (see Figure 2.24). Therefore storage at ambient temperatures is notrecommended.


0.02

0.04

0.06

0.08

Rat

e of

dim

er fo

rmat

ion

(%/d

ay)

0 10 20 30 40 50 60 70

Temperature (°C)

Figure 2.24 Pure MDI: rate of dimer formation. This diagram is based on infor-mation made available by BASF Corp., USA

Even at the recommended storage temperatures, slow dimerization will occur,resulting in cloudiness developing in the molten product. Table 2.9 (Dow,1986) illustrates the approximate times, including the time in the supplier’swarehouse and during transport, that pure MDI can be maintained at the giventemperature before cloudiness develops. Users of pure MDI will, therefore,need to assure themselves that the material is not stored for long periodsbefore use. In-line filters can be used to remove small amounts of solid thatmay have developed.

Table 2.9 Approximate storage lifeof pure MDI in the liquid state.

Temperature Storage life

◦F ◦C days

105a 40.6 31110 43.3 35115 46.1 35120 48.9 28

aAs this is essentially the melting point ofpure MDI, storage at this temperature is notrecommended.

Intermediate bulk containersRe-usable intermediate bulk containers (IBCs), typically containing 1000 l, arecommonly used for the delivery of both TDI and polymeric MDI. Pure MDIis not delivered this way because the IBCs are unheated and the MDI wouldsolidify. The containers are used on-site for the storage of the diisocyanatesand, when empty, are sealed and returned to the supplier for refilling. Theyare a very convenient way of handling diisocyanates for relatively small oper-ations. The advantages include easy connections into processes and the simplereturn of the container for refilling without the cost and inconvenience of drumdisposal. These containers have bottom run-off valves and can be connectedup to machine tanks, thus avoiding the need to handle drums. A top-mounteddessicant cartridge dries the air that enters the container on discharge of the


diisocyanate. Diisocyanate suppliers should be consulted on the best type ofcontainer for a particular manufacturing situation.

Drums and pails: melting outA considerable quantity of MDI and TDI is delivered to users in drums.The drums are predominantly of capacity approximately 200 litres (55 gal).Smaller containers (for example 1 gal pails) and cans of different sizes (forexample 18 litres) are also available in different parts of the world. It is par-ticularly important that the correct methods for handling, storing and usingdrums and cans are understood in order to maintain product integrity and toavoid releases of vapour or liquid.

Any warehouse used to store polymeric MDI or TDI drumstock should bewell ventilated and, ideally, maintained at 20 to 25 ◦C (68 to 77 ◦F). The diiso-cyanates must not be stored with flammable materials, foodstuffs or corrosivematerials. Drums should be stored palletized in an area that will contain anyleaks; they should not be stored on earth floors. Drums should not be storedmore than three high unless they are palletized.

Ideally, drums of polymeric MDI or TDI are stored inside to avoid extremesof temperature. However, if they are stored outside, exposure to direct sun-light and rain should be avoided. As drums of polymeric MDI or TDI mayhave been exposed to cold conditions during transport, the contents may bepartially or completely solidified. Drums containing solidified material can beleft in a warm room until the diisocyanate has melted. Alternatively, solidifiedpolymeric MDI can be melted using the procedure described below for pureMDI. The contents should be well mixed before use.

Pure MDI is usually transported in drums in refrigerated containers at −20to 0 ◦C (−4 to 32 ◦F) to prevent dimerization. Frozen drums should be storedimmediately upon arrival in a refrigerated storeroom. A uniform temperatureideally below 0 ◦C (32 ◦F), and preferably lower, should be maintained. Thiswill depend on the period of storage and the intended use. Temperatures mustnot be allowed to fluctuate widely if dimer formation is to be avoided. Drumsof solid pure MDI should be used as soon as possible after delivery. Prolongedstorage, even in refrigerated stores, can lead to a slow build-up of dimer.

Table 2.10 (Dow, 1986) shows approximate storage times for pure MDI inthe solid state before cloudiness develops on melting. These times include thetime the product has been in the supplier’s warehouse and the time duringtransport assuming that the temperatures stated have been maintained.

Table 2.10 Approximate storagelife of pure MDI in the solid state.

Temperature Storage life

◦F ◦C days

0 −17.8 300+10 −12.2 210+39 3.9 68+50 10 33


Drums of solidified pure MDI, or products containing pure MDI, can bemelted in a number of ways. However, because of the potential for dimeriza-tion, it is important to accomplish the melting procedure as quickly as possiblewhilst avoiding excessive local temperatures. The methods of heating pureMDI that are recommended by the manufacturers are the use of a hot-air oven,a steam chest or hot water bath. The highest heat transfer rate is obtainedusing a steam chest, hot water bath or a high humidity steam-powered oven.To improve the heat transfer and reduce the melting period, the drums maybe rotated. When a hot air oven is used it should be well ventilated and thetemperature should be within the range 70 to 80 ◦C (158 to 176 ◦F), or as indi-cated for the specific product in the product data sheet. Complete melting ofthe drum contents under these conditions may take up to 15 h. Electric drumheaters or other direct heating methods such as open flames or hot plates mustnever be used, as they would create local hot spots in the drums and henceexcessive dimer formation. Whatever method of melting is chosen, drumsshould always be inspected carefully prior to melting. Any drum having sig-nificant damage should be marked appropriately and put to one side for laterattention. If a drum bulges significantly because of excess internal pressure itrequires emergency handling. Refer to Key Theme 6, Dealing with accidentsfor further guidance.

It may be necessary to provide a means of releasing any pressure that mightbuild up during melting. A pressure relief valve may be used to prevent entryof moisture. This must have a carbon cartridge to adsorb emitted vapours. Thevalve must be inspected and cleared of any blockage prior to heating. A furtheroption is to use a pipe nipple with a ball valve, but this needs to be openedmanually to release pressure. Valves should be removed before the cooling ofmelted MDI in a drum is complete to prevent a vacuum developing in the drum.

The diisocyanate may be inspected with a light and, if necessary, stirredto confirm that no solids remain and that melting is complete. Atmosphericmonitoring should be conducted at regular intervals to ensure that the extrac-tion system is working efficiently. After melting, the drum contents shouldbe mixed thoroughly to homogenize them; this may be achieved by rolling.The product can be allowed to cool to the correct processing temperature forpolyurethane manufacture before use. If small-scale processing is intended, itis recommended that the drum contents should be melted and split into smallerquantities which can be frozen and melted out again separately when required.It is very important to homogenize the contents of the drum before splittingthe contents. This procedure will prevent repeated melting and cooling of theproduct, and thus will minimize chemical degradation. Once a small quantityhas been re-melted, it should not be further solidified and melted.

If a small quantity of finely-divided, insoluble material is present it maybe removed by filtering through an in-line filter. A stainless steel vessel witha polypropylene filter bag is suitable. The lines should be heated and blownclear with nitrogen after use. Small amounts of finely-divided insoluble solidsdo not normally cause difficulties in handling or product performance.

Emptying of drumsThe contents of diisocyanate drums are usually transferred to machine tanksor intermediate storage tanks. This should be done by using pneumatic (or


Nitrogen inlet ordryer-breathervent

Ground (Earth)strap

Pumpwith motor

Toprocess

Figure 2.25 Drum unloading pump

electric) drum pump (Figure 2.25), or by using an electric standing pump withflexible dip tube inserted through the bung hole to minimize exposure. Thearea needs to be well ventilated and protective clothing should be worn.

Ideally, the drum pump or dip tube should be transferred direct from theempty drum into the contents of the next full drum, to prevent the ingress ofair and moisture into the equipment. Drum pumps soon seize up if they are notprotected from polyurea formation. It is not recommended that diisocyanatesbe poured direct from a drum into a tank. Spillage can easily occur even whenthere is lifting tackle.

It is very dangerous to pressurize diisocyanate drums to effect pres-sure transfer of the contents. Drums are not designed to withstand pressuretransfer, and drum rupture may occur.

When drums are emptied with drum pumps or dip tubes, the back-flow fromthe dip tube, together with the residues on the walls and sides of the drum,can result in up to 5 kg (11 lb) of residual diisocyanate. If a nonreturn valveis installed at the bottom of the dip tube, the residual diisocyanate can bereduced to 400 to 1000 g (0.9 to 2.2 lb). Residues should be removed fromdrums before the drums are further processed. It is important to minimize thevolume of the contents to facilitate their safe disposal.

Two suitable devices for draining drums and retaining their contents areshown below (Figures 2.26 and 2.27). Local ventilation should be providedand suitable protective clothing should be worn to prevent skin contact. InFigure 2.26 the inverted drum is secured in a frame. An attachment with aball valve allows diisocyanate to be drained into the next drum of material tobe used or a waste disposal container. The attachment screws into the bunghole of the drum and connects directly into a modified bung ensuring a tightfit with the receiving vessel. In Figure 2.27 the emptying device has a slopedplatform provided with a protruding ring to allow central positioning of thedrum and a funnel to receive the diisocyanate. The close contact of the ring


250

mm

Safety chain

Residue

3/4" Bung

2" Bung

3/4−1/4" Reducing piece

1/4" Ball valve

1/4" Tube

200 mm

Figure 2.26 Emptying of MDI/TDI drums (1). Reproduced with permission fromGuidelines for the Responsible Management of Empty Diisocyanate Drums(ISOPA, 1997)

600 mm

900

mm

3/4" bung

5°

20 m

m

Figure 2.27 Emptying of MDI/TDI drums (2). Reproduced with permission fromGuidelines for the Responsible Management of Empty Diisocyanate Drums(ISOPA, 1997)


and the open side of the drum prevents release of diisocyanate vapour duringthe draining process.

All drums should be drained at between 20 and 30 ◦C (68 to 86 ◦F) forabout 2 to 3 h or until they are drip free. Pure MDI in drums should be drainedbetween 45 and 60 ◦C (113 to 140 ◦F). This has to be done inside an oven andcan generate a potential vapour risk. After thorough draining, the drum willretain residues of about 60 g of TDI or about 300 g of a highly viscous MDIprepolymer as shown in Figure 2.28.

(A) MDI (Prepolymer)(1990 mPa s)

(B) PMDI(550 mPa s)

(C) MDI(2,4′/4,4′

eutectic mixture)(12 mPa s)

(D) TDI (T80)(3 mPa s)

Diisocyanate viscosity in millipascal seconds

0

100

200

300

400

500

600

700

800<1000

300

200

750

400380

10060

Pump with non-return valve

"Drip-free"

Res

idue

(g)

Figure 2.28 Drum residues from four diisocyanates at 25 ◦C. Reproduced withpermission from Guidelines for the Responsible Management of Empty Diiso-cyanate Drums (ISOPA, 1997)

Empty drums should be well sealed to prevent moisture ingress, until theyare processed further. This may involve sending them to a specialist drumprocessor or decontaminating them locally: in either case the original labelshould be left on the drum to advise the workforce of potential risk of handling.See Key Theme 3 for details on drum decontamination. Empty drums shouldbe inspected regularly for signs of pressure. If a drum is found to be bulging itshould be treated as a potential emergency. Immediate action should be takenas indicated in Key Theme 6: Dealing with accidents.


Taking samplesIf a small sample of diisocyanate is required for quality assurance, it shouldbe provided by the manufacturer. However, if it is necessary to sample a smallquantity of diisocyanate from a drum, it can be drawn off conveniently bypositioning the drum horizontally and using gravity discharge. The method isdescribed in the box. Once a drum has been opened, adequate precautions mustbe taken to prevent the entry of moisture.

Taking samples from a drum

Stand the drum head uppermost. Remove the two seal caps andremove the 3/4 inch diameter bung. To the 3/4 inch bung hole fit anelbow of piping, with a hand-operated valve to contain the contentsof the drum during tipping, and a silica drier to prevent water ingress.Remove the bung from the 2 inch diameter bung hole and fit a gatevalve or PTFE-lined diaphragm valve. With the valve closed, lowerthe drum into the horizontal position on to a suitable drum stand ortrolley. A drip tray containing solid absorbent and adequate suppliesof liquid decontaminant should be available. A bund (dike) to containspillages is desirable.

Safety issues in workplacesusing MDI and TDI

MDI and TDI are used in many dif-ferent types of polyurethane manufac-turing processes. Most such processesinvolve the mixing and dispensing ofcarefully measured quantities of reac-tion components, comprising a diiso-cyanate, and a polyol with other ingre-dients such as catalysts and surfac-tants. These reaction components are

measured and mixed, continuously or discontinuously, using high pressureimpingement mixing heads or low pressure mechanical mixing heads, or bybatch mixing techniques. Several common polyurethane manufacturing pro-cesses are illustrated in Figure 2.29.

The three principal ways in which workplace exposure to emissions of MDIand TDI can be minimized are by:

• good engineering design of the equipment and the systems used to handlethe diisocyanates, to minimize releases;

• the use of appropriate ventilation systems;• good working, housekeeping and waste disposal practices.

Good engineering designProcesses should be designed for:

• safety;• minimization of releases and pollution;• compliance with regulatory requirements;• smooth throughput of products;• ease of operation and observation;• easy access for maintenance;• easy access for charging tanks;• simplicity;• cleanliness;• waste minimization.

Good design of manufacturing processes reduces breakdowns, maintenance,and process deviations and hence the need for operator intervention, resultingin reduced risks and reduced use of protective equipment. Good operational


Side paper Mixing head

Transport device

Bottom paper

Continuous production of flexible foam slabs

1

1

1

1

1

1

2

Discontinuousfoaming process1) With bulkhead construction2) With high output foam machines having a movable mixhead fitted with a flexible hose

45° ca.2.50 m

1. Mould2. Mixing head

Manufacture of panels for refrigerated trucks

Machine with moving moulds and fixed mixing head

Flexible facingmaterial on coil

Double conveyor belt

Mixing head

Cutting device

Double conveyor technique for productionof rigid foam laminates

Spray-insulation of pipes with rigid urethane foam

Injection

Pressmould

Distribution manifold

Reaction injection moulding process

Storage conditioning

Finishedpart

Figure 2.29 Some polyurethane manufacturing processes. Reproduced with permission from the handbookBayer–Polyurethanes, 1979


procedures eliminate the need for operators to work in areas of high diiso-cyanate concentration. There can be considerable saving in effort and moneyif a safety measure is an integral part of the design rather than an additionalhighly instrumented system requiring its own separate maintenance, trainingand supervision. If a risk is identified it is always worth reviewing the basicdesign that gives rise to that risk, to see if the risk can be removed at source.Engineering solutions should be sought for plants that require workers to enterenclosed areas frequently. This may mean, for example, designing externalcontrols, using more reliable seals and gaskets and provision of automatedsample taking rather than adding a ventilated enclosure for manual sampling.

Liquid releases may be minimized by:

• Using closed liquid transfer systems from bulk storage to the process-ing machinery. In-line metering of chemicals removes the need for man-ual weighing.

• Using glandless, canned or fully immersed pumps to minimize leakage.• Installing pumps and other items of equipment in positions for easy access

for maintenance.• Ensuring that lines transferring chemicals have a minimum number of joints.

Joints should not be threaded, and they should be provided with spill pro-tection where necessary, since leaks can sometimes occur at joints.

Pipework for MDI and TDI transfer should be all-welded with bolted flangeconnections using gaskets of Viton, Teflon or nitrile rubber where practi-cable. Manual feeds should be minimized. Feed valves should be interlockedto prevent mis-feeds, mis-sequencing of raw material stream or spillage of themix. For liquid leaks, such as those caused during disconnection of lines, hosesand filters, there need to be drip trays, bins, sealed floors or other measures.Filters and connections should be within their own enclosures and providedwith local exhaust ventilation.

Ventilation controlControl of diisocyanate vapours and aerosols is usually carried out by meansof a suitable exhaust ventilation system. To minimize worker exposure to MDIand TDI vapour releases during the processing of polyurethanes, it is desir-able to enclose the processing equipment as much as possible and to removethe releases by adequate ventilation. Good enclosures and properly designedcovers, and segregation of parts of the process by internal screens, allow theprincipal sources of releases to be localized, so that the ventilation systemcan be kept to a minimum size, complexity and cost and still be efficient.Ventilation can be considered in terms of the following three categories:

• total enclosure, with local ventilation if necessary;• partial enclosure, with local ventilation;• no enclosure, with local ventilation.

There will need to be openings in all polyurethane processes. In a nominallyfully enclosed manufacturing process, such as reaction injection moulding, thematerials injected into the mould will displace air through vents. The displaced


air may possibly carry with it some diisocyanate vapour or aerosol. In the man-ufacture of flexible foam slabstock considerable quantities of diisocyanate willprobably be present above the rising foam and these will need to be containedand removed. Full enclosure is not a practical option since most of the pro-cesses require openings in their enclosures to allow entry or exit of movingparts. In these cases the preferred choice is to enclose the process as fully aspossible and use ventilation to control and minimize releases from the enclo-sure to the workplace. Extraction of contaminated air is most effective when adirected source of fresh air is also provided to ensure preferred directional aircurrents. Local ventilation will work best if it assists the natural flow of thevapours and aerosols, is close to their source, and is located so as to receivethem. Broadly speaking, releases from warm moulds and warm rising foamwill tend to rise with the associated warm air, while spray aerosols will tend tosink or travel with the air flow. The vapour density of the exhaust gas is virtu-ally the same as that of air at the same temperature, as the diisocyanate vapourconcentration is always extremely low. In a tunnel enclosure, the extract ductsshould be located so as to give adequate inward flow through the openingswhile disturbing the process as little as possible. The ducts should be locatedto avoid producing a strong draught inside the enclosure over the rising foamunless it is required to remove fumes for other reasons, such as explosioncontrol if certain solvents are present.

Jet flows (fast-moving, directional air streams) carrying aerosols may arisein certain operations, notably in spraying but also in applications in which airis expelled rapidly from mould vents. To achieve highly effective extraction,it is essential to accommodate these powerful jet flows by aligning ventilationoutlets with them. Moving machinery can also cause jet flows. Cooling fans onmotors can create draughts. Disc and band knives can establish very strong jetflows as air is entrained by the moving blade. If necessary, smoke canisters orsmoke candles can be used to establish the direction and speed of movementof jet flows.

To maximize the removalof releases the exhaustventilation usedshould be:

• inside a well-designedenclosure;

• placed so as to assistthe natural direction oftravel of the release;

• placed close to thesource of the release;

• capable of dealing withjet flows.

The rate of air flow shouldbe monitored anddisplayed.

For some processes options for enclosure are limited because of the spacerequirements for access or movement of parts. An example might be the pour-ing of reaction mix into open moulds mounted on a carousel. Partial enclosurerequires more extraction than total enclosure because of the proportionatelylarger open face. The effect of increased air removal is to make it more diffi-cult to control the temperature in a partial enclosure than in a full enclosure.Furthermore, the extraction has to be in the right place because, unlike fullenclosure, it is unacceptable for the enclosure itself to be full of vapour.

Local exhaust ventilation without enclosure and general (dilution) ventilationare the least effective means of collecting and controlling releases. Addition-ally, where abatement or clean-up treatment of the exhaust air is needed beforedischarge to atmosphere, such ventilation provides the largest volume and mostdilute mixture to the treatment plant. This increases the treatment plant sizeand running cost, and reduces its efficiency. The cost of heating air to replacethe air extracted can also be very significant. However, if releases are known tobe at a low level, local exhaust ventilation with or without enclosure and goodgeneral workplace ventilation can adequately protect workers (Figure 2.30).

Most enclosures are too small for entry, but operators may still be able tolean in. Access to a working enclosure should be restricted, or even prevented,


Figure 2.30 Local ventilation over a diisocyanate-containing drum

in normal use. When access is required for maintenance or other work thereshould be strict personnel control. Good visibility into the enclosure reducesthe need for access, as does good process design. Processes should not requiremanual transfers of components into or out of enclosures.

Vapour releases from operations using MDI or TDI will be almost invariablyat concentrations considerably lower than those of their saturated vapour, andhence not liable to condense in ducting. The duct velocity is not crucial, andthe limit is likely to be defined by the balance of airflow noise, power loss inthe ducting and excessive size of the ducts if the duct is enlarged to reducenoise and power loss. Some operations give rise to aerosols, particularly ofreaction mixture. Design of ducting will need to take account of the presenceand size of aerosol particles: the larger the particle the more likely it is todeposit onto sharp bends in the ducting. Where foaming mix is depositedon ducting polyurethane foam may collect and build up altering ventilationcharacteristics, and may even cause blockages over a period of time.

In cutting and trimming, where dust may be generated, the ducting can use-fully incorporate a wider section and waste bin to collect heavier particles near


the source of the dust. The duct should thereafter have a diameter calculatedto give a duct velocity of 10 to 20 m/s (2000 to 4000 ft/min) greater than thetransport velocity of the dust produced. Where deposition of dust, solvent oraerosols of reacting ingredients is foreseeable, the ducts will need to haveaccess for cleaning, and possibly drainage points.

The need for indicators of air flow will have to be judged in the light ofcurrent best practice, local legislation and the seriousness of the consequencesof lack of ventilation control. One very simple device is a hanging strip of paperor fabric in front of the ventilation intake, although it shows only that thereis some extraction flow. On modern block foaming plants enclosed in tunnelsa fall in air flow, detected by pressure differential or other devices, raises analarm and stops the chemical feeds. Such devices are becoming increasinglythe standard on extracted spray booths.

Spraying polyurethane foam insulation in a confined, inaccessible area withonly a low level of local ventilation available requires operators to wear afully protective suit including supplied-air respiratory protection. Unprotectedpeople should be excluded from the high exposure area until safe conditionshave been established.

Good working, housekeeping and waste disposal practicesGood working practicesMixing of the reaction streams in polyurethane processes can be achieved bylow pressure mechanical mixing or by high pressure impingement mixing. Inlow pressure mixing equipment, a mixing head of a relatively large volumecontaining a rotating stirrer is used in order to obtain continuous efficientmixing of the components (Figure 2.31). In order to clean the equipment atthe end of the dispensing operation all chemical streams can be closed downexcept the polyol stream, which then removes residues of all other chemicals.Alternatively the mixing head can be flushed through with a solvent to remove

Reactioncomponents

Reactioncomponents

A wide variety ofstirring device designsis available. Mixinghead capacities varyfrom a few cubiccentimetres to aboutone litre. Severalseparate streams ofreaction componentscan be meteredindividually to themixing head.Mixed reaction

ingredients

Figure 2.31 Low pressure mixing


any residual polyurethane material, followed by an air blast to remove theresidual solvent. This action can lead to emissions of diisocyanates and solventvapours. It is essential that all rinsing and cleaning operations are done into acontainer fitted with its own extraction facility. It is also strongly advisable tolink the solvent flush and air blast, so that air cannot be put through a headbefore the solvent flush.

The alternative technology employs high pressure dispensing equipment(Figure 2.32). This technique uses piston pumps metering the chemicals undera pressure of 150 to 200 bar (2175 to 2900 psi). Mixing is carried out in a verylow volume chamber where the atomized chemical streams mix by impinge-ment. The mixing head is self-cleaning, being fully purged by means of a closefitting plunger at the end of each shot. One great advantage that high pressuremixing heads have over low pressure heads is that solvent and air blasts arenot needed.

Principle of the Krauss-Maffei mixing head

Mixing headin dispense mode

Mixing headin recirculation mode

Hydraulicoperatingcylinder

Polyolrecirculation

Diisocyanateflowing to themixing chamber

Diisocyanaterecirculation

Polyol blendflowing tothe mixingchamber

There are many designs of high pressure mixing head. Most arecharacterised by recirculated reaction streams prior to mixing, andby piston cleaning at the end of dispensing the reaction ingredients.

Figure 2.32 High pressure mixing. Reproduced by the kind permission of Hunts-man International

Adequate personal protective equipment needs to be provided for all expectedsituations in the workplace, including emergency situations, and staff must betrained in its use. It is important for managers to ensure that the equipment isactually used, and that it is maintained.

As minor drips and leaks of diisocyanates are possible in a number of work-place operations, an adequate stock of neutralizer and absorbent solids fordiisocyanates should be readily available and staff should know where they areand how they should be used. Neutralizer will also be necessary to deal withused drums, machine parts and contaminated clothing. Contaminated clothingmust be changed immediately if it becomes contaminated with MDI or TDI toprevent skin contact. After spills and leaks are dealt with, workplace air should


be monitored to ensure that the occupational exposure limits for diisocyanatesare not exceeded.

Maintenance tasks may take place outside normal working hours when theremay be limited support available in case of problems. Maintenance, such asbreaking open lines or dismantling pumps containing diisocyanates, can involvepotential exposure. It is, therefore, particularly important that all staff involvedin maintenance activities are made fully aware of the potential dangers, andare fully equipped with appropriate personal protective equipment.

Diisocyanates usually react very rapidly during polyurethane manufacture,particularly when catalysts are used. Despite this, very small amounts of excessMDI or TDI may remain unreacted during the curing process in foams andother products, and polyurethane products should be handled with cautionuntil it has been established that no atmospheric or skin contamination occurs.In any event, it is important to wear gloves when handling freshly madepolyurethanes to avoid possible skin contamination. Any residual diisocyanateusually disappears due to completion of the polyurethane reaction, by reactionwith atmospheric moisture or by reaction with the polyurethane itself. TDIwas not detected when air was passed through cured flexible foam for beddingthat had been made for 3 days, even when extremely sensitive tests were used(Hugo et al., 1997).

During the period of final cure, finished products should be stored in well-ventilated areas unless it is known from air measurements that the diisocyanateis no longer being liberated. Polyurethanes made in large blocks, such as flex-ible foam slabstock, may retain heat for many hours because of the insulatingproperties of the foam. Such blocks should not be stored close to each other toallow heat dispersion, and fire prevention systems must be installed. If post-manufacture fabrication is undertaken on freshly made polyurethanes, workersshould be protected from possible diisocyanate exposure by ventilation of theworkstations.

Local measurements of diisocyanate concentrations in the air should be car-ried out if there is any doubt about the need for supplementary ventilation. Inaddition to diisocyanates, there will often be additives in the polyurethane for-mulation such as catalysts, including tertiary aliphatic amines, fire retardants,surfactants and blowing agents. Some of these substances may also be suffi-ciently volatile to add to the ventilation requirements necessary in the storageand fabrication areas, particularly in the case of open-cell flexible foams.

There are several industrial operations in which cured polyurethanes may besubject to degradation due to the effect of heat (thermolysis). These include:

• hot wire cutting of flexible foam;• hot air welding of flexible foam and polyurethane elastomers;• flame lamination of flexible foam;• sawing of rigid foam;• sanding of rigid foam.

Gaseous breakdown products resulting from thermolysis have been studied,see, for example, the abstracts of the Isocyanate 2000 Symposium (Isocyanate2000, 2000). The dusts from some of such operations have been analysed forresidual isocyanate groups. This is a complex field, with many outstanding


questions on analytical methodology, the effect of different thermolysis con-ditions, the formulae of the foams and associated risk assessments.

Those involved in such operations should be protected from exposure tothermolysis gases and dusts by the use of effective engineering measures tominimize exposure, but preferably by changing the process to achieve theeffect without thermolysis. For example, hot wire cutting has been replacedby sophisticated cutting devices such as band saws, oscillating saws and highpressure water jets, from which levels of emission breakdown products areextremely low.

Exposure to toxic combustion gases can arise from polyurethanes beingburned in unsuitable devices. Diisocyanates may be released from burningpolyurethanes, in addition to the normal and expected combustion gases(i.e. carbon monoxide, carbon dioxide, nitrogen oxides and hydrogen cyanide)from any natural or synthetic material containing carbon and nitrogen, suchas wool, silk, nylon and acrylic fibres, and ABS. Accordingly, all incinerationshould be carried out by specialist companies. It is important to ensure thatpolyurethanes are not allowed to burn in open fires.

Good housekeepingGood housekeeping requires working procedures, training and resources tobe both provided and implemented as part of the safety system to ensureclean working conditions and the adequate maintenance of production andsafety equipment.

• Define limited areas where diisocyanates are stored separated from otherchemicals. It is important to isolate the diisocyanate storage areas from thepolyurethane production areas.

• Ensure that MDI and TDI are always stored in clean, closed containers.• Ensure that every drum is correctly labelled and that the label clearly

describes the contents.• Minimize the number of partly used drums.• Prohibit eating, drinking or smoking in the workplace where diisocyanates

are used: separate areas should be provided. Encourage personal cleanliness,especially when taking a break from work.

• Keep machinery and other equipment clean and decontaminated when notin use. Solvents that are increasingly used to clean contaminated equipmentinclude N -methyl pyrrolidone and ‘dibasic ester’ (a technical product madefrom mixed dibasic carboxylic acids). If solvents are used during the cleaningprocess, prevention of skin contact is particularly important.

• Traces of diisocyanates should not be left on work surfaces, floors or externalmachine parts. They may contribute to inhalation exposure, or cause skincontamination.

Good waste disposal practicesDecontamination of drumsThis should be undertaken as soon as possible after removal of the contents.Drums must be drained before decontamination, and then stored upright for atleast 2 h to allow product to drain from the drum wall to the bottom. Drums


should be decontaminated at 20 to 25 ◦C (68 to 77 ◦F). Diisocyanates havinga viscosity of greater than 150 mPa s, such as polymeric MDI and prepoly-mers, should be maintained at 25 to 30 ◦C (77 to 86 ◦F). Pure MDI mustbe neutralized at 45 to 60 ◦C (113 to 140 ◦F). An oven should be used forwarming the diisocyanates. Diisocyanates are neutralized as described in KeyTheme 3.

Decontamination of drums

Drain drum until drip-free

Add neutralizer liquid (see Formulations 1and 5 in Key Theme 3)

Roll the closed drum at least four times

Open drum (CAUTION: excess pressure may be present!) and leave with a loose-fitting lid until all the reaction is completed.

Close drum and dispose of contents and drum in approved manner

Once drums are decontaminated and all reactions have ceased the drumsshould be closed tightly. Labels should be attached indicating the contents ofthe drum and its status as decontaminated. A certificate of drum decontami-nation accompanying the drums to the reconditioner is strongly recommended(see Key Theme 3 ). Drums that have been decontaminated will contain neu-tralized diisocyanate, and residual neutralization solution and can be handledby a specialist drum reconditioner or metal recycler. Decontaminated drumsmay be used for scrap metal, or may be reused after reconditioning. As alast resort they may be sent to landfill after removal and safe handling of thewaste neutralizate. Drums for landfill should be punctured or crushed beforedisposal to prevent re-use. The re-use of drums that have not been completelydecontaminated is potentially very dangerous. For example, the re-use of TDIcontainers to transport nontoxic materials is reported to have led to illness in40 workers in a plant making surgical gloves from rubber latex (Siribaddanaet al., 1998). Used drums, even if believed to be diisocyanate free, must neverbe used for domestic purposes such as a barbecue, domestic incinerator ortrash receptacle.

Under no circumstances should hot torches be employed to cut up useddrums, since such drums may contain residues of MDI or TDI.

In many countries there are qualified drum reconditioners and recyclers whowill clean the drums before reconditioning, or who will reclaim the drum for


its metal content. It is important to select a company that has the full local andnational authority approvals necessary for processing and disposal of wasteproduct residues, and for the transport of the drums.

Diisocyanate suppliers may be able to provide the names of suitable com-panies. When possible, the company should be audited and approved for drumreconditioning or recycling. The methods used for disposal of waste residuesshould also be examined. Regulations and commercial practices vary fromcountry to country. Local enquiries should be made before drum disposal pro-cedures are established.

Sources of information ondrum reconditioners are:European Federation ofDrum Recyclers, SERRED;The Association ofContainerReconditioners (USA).

Disposal of diisocyanate wasteWaste diisocyanate may be collected until there is a sufficient quantity fordisposal by a specialist contractor. However, a small amount may be conve-niently handled on site. There are three basic methods of disposing of liquiddiisocyanate wastes. These must be considered in the light of local regulations.The choice of method will also depend upon the amount of waste to be treated.The methods below are discussed in Key Theme 3 in more detail.

1. Reaction with liquid neutralizing agentThe diisocyanate is added slowly to the neutralizing agent while stirring inan open-topped vessel such as a drum. To ensure a complete reaction theproportion of neutralizer to diisocyanate should be 9:1. Any waste solventscontaining diisocyanates must also be treated to neutralize the diisocyanatebefore the solvents are disposed of.

Disposal of diisocyanate waste

Neutralize diisocyanate waste using 0.2 to 2 % liquid surfactant

Leave in drum with loose-fitting lid, until reaction completed.

Dispose of alkaline waste.

5 to 10 % sodium carbonatewater to make up to 100 %.

2. IncinerationThis should be carried out only in properly supervised facilities specificallydesigned for the disposal of noxious chemical waste.

3. Reaction with waste polyol blendThis is normally used only after machine calibrations when the meteredamounts of diisocyanate and polyol blend can be reacted together to givea polyurethane. This should be undertaken with great caution (see KeyTheme 3 ).


Safety issues in some important polyurethane processesFlexible polyurethane foam slabstock productionThe flexible foam slabstock process (Figure 2.33) is an excellent example ofthe continuous developments in engineering control, which have led to reducedreleases into the workplace. In this process, the foam mix is dispensed onto acarrier paper on a conveyor which draws it through a ventilated tunnel withthe rising foam. As the foam rises it is contained within side-papers runningalong sidewalls. Once the block is self-supporting, all papers are removedand disposed of. Innovations in the process which relate to safety have beenthe use of a top paper and the use of polythene sheeting between the risingfoam and side-papers. The former reduces releases of TDI vapour from thefoam surface. The latter prevents uncured flexible foam, with high TDI levels,from soaking into the paper. The handling of such saturated papers can be asignificant source of potential exposure of workers to TDI. When polythenesheeting is used it does not need to be removed until the foam has cured. Theventilated tunnel has openings at the start and exit to accommodate the paperfeed and conveyor with the emerging foam block.

Figure 2.33 Flexible polyurethane foam continuous block plant (figure by courtesy of Cannon Viking Limited,UK)

Openings for inspection and sampling should, wherever possible, be self-closing or linked to an alarm warning system or both. There should be extrac-tion on the tunnel enclosure applied near entry and exit so as to provide anadequate inflow of air at the openings. The extraction air flow depends onthe process parameters, such as the size of openings, the rate of chemicalthroughput and the rate of rise of the foam. It should be, typically, at least


0.3 m/s (1 ft/min) inward for well-designed small openings liable to be open atany time. A higher airflow rate, 0.5 to 1.0 m/s (1.6 to 3.3 ft/min), is appropriatefor large openings close to vigorous sources of emissions. Only a small quantityof diisocyanate vapour is emitted at the pouring point or trough. However, atthis point a very large volume of air is being drawn into the extraction systemand this prevents escape of airborne diisocyanate from the head of the tunnel.

The enclosure should be well lit internally so as to reduce the need forobservers to approach windows or openings too closely. Operators requireaccess before and after each run to service the mixing head, but during runsdirect observation may be achieved through windows into the highly illumi-nated tunnel or by closed circuit TV cameras. Note that if the lighting is throughtransparent panels from external light sources, the cost of the installation isreduced and it is much easier to clean and maintain. Workers should not touchnozzles, or enter the foaming tunnel enclosure, or deal with the paper removalwithout extensive personal and respiratory protection.

The efficiency and effectiveness of an enclosure can be improved by attentionto design detail. The number of openings should be minimized and the riskof turbulent air currents of contaminated air escaping from the main foamentry point can be reduced by profiling the opening so that there is a smoothtransition into a short entry tunnel. Waste bins should be incorporated insidethe enclosure to contain any waste generated. Sometimes a negative pressureindicator or loss of negative pressure detector is installed in the tunnel to givea warning alarm.

Flexible foam slabstock can also be made discontinuously (Figure 2.34).Here also excellent ventilation arrangements are necessary (not shown in thefigure) to protect workers from exposure to diisocyanates.

MAX LEVEL

CAPACITY 113 LITRES

TIN

Figure 2.34 Flexible polyurethane discontinuous block plant (figure by courtesy of Cannon Viking Limited,UK)


Polyurethane foam moulding processesA typical example of this type of process is polyurethane foam mouldingwhere open moulds are transported past fixed operating stations (Figure 2.35).A production cycle consists of

• cleaning the mould;• spraying on release agent;

(a)

(b)

Figure 2.35 Car seat moulding line: (a) polyurethane mixing head above an opencushion mould; (b) operator removing poyurethane cushion from mould. Figuresreproduced with permission from British Vita Plc


• dispensing the reacting polyurethane foam mixture into the heated mould;• closing the mould;• allowing the foam to cure, sometimes in a heated tunnel;• removing the moulding from the mould, often aided by a compressed air gun.

Efficient ventilation (Figure 2.36) is needed when applying release agents,dispensing the polyurethane mixture, closing the mould and demoulding. Therecontinue to be improvements in mould release technology, notably in a reduc-tion in the frequency of application of release agent and the use of water-borne,rather than solvent-borne, systems.

Transparent panel

Hood

Figure 2.36 Spraying of release agent into a mould

Low pressure mixing heads need to be cleaned at intervals and sufficientventilation is also required for this operation. High pressure mixing headswould not normally need to be cleaned. When moulds are used there may be abrief potential exposure peak as the mould lid closes, particularly when TDI isused. It is important in this case to provide ventilation at this point. To providesufficient ventilation at all these stages of the process requires careful designof the enclosures, including limiting the need for access for manual operations.The mould can be closed automatically or by remote control, and transportedthrough the curing tunnel. The cured foam can be demoulded remotely. Opera-tor contact with the process can thus be minimized and exposure to the possibleemissions reduced. The highest potential exposure of operators is liable to beat the stages of dispensing, mould closure, the displacement of air from themould during foam rise and manual demoulding.

Reaction injection moulding (RIM) in closed moulds is also widely used,particularly with fast-reacting MDI-based systems. In this process the reactioningredients are mixed by high pressure impingement. The high pressure mixinghead is an integral part of the closed mould and the reacting ingredients areinjected into the mould cavity. A vent hole allows air to be displaced from


the mould. The moulds may be stationary or may move mechanically to themixing head. Worker exposure to the reacting chemicals during RIM processingis extremely low. Care is usually necessary on demoulding the finished parts,though fast reacting systems have very little free MDI on demoulding.

Production of rigid polyurethane foam panelsby a continuous processIn this process an MDI-based rigid foam reacting system is deposited onto acontinuous moving substrate such as paper or steel. The foam mixture reactsand rises, comes into contact with a second facing material and forms a contin-uous polyurethane foam laminate (boardstock). The facing materials are oftenheated prior to contact with the foam mix to improve surface cure, increasingthe potential exposure.

The even distribution of reacting foaming mixture on the substrate is criticalto the process because the mixture expands to typically 30 times its initialvolume. Originally, the best method to achieve such a layer was by meansof a traversing spray head. This produced aerosols and splashes of reactingchemicals, which resulted in risks to the operators and could lead to deposits inducting which had to be removed frequently. Engineering solutions have beenfound to overcome these problems. A pour laydown using a traversing pipe isnow commonly used. This technique produces narrow bands of reacting liquidfoam, which merge together during the ensuing process, eliminating splashingand aerosols. In another approach the foam mix is enclosed between the twofacing materials before it begins its reaction. Due to the complete enclosureof the reacting foam between the facing materials, MDI emissions are greatlyreduced. It is still necessary to enclose the foam laydown and conveyor areain a ventilated tunnel.

Spraying of polyurethane systemsTwo-pack diisocyanate-based paint spraying and rigid foam insulation are typ-ical examples of diisocyanates in spray applications. These applications areoften carried out in controlled factory environments where engineering precau-tions can be taken to prevent worker exposure. Certain applications of rigidfoam spraying have to take place away from a factory and special precautionswill be necessary to protect those involved. Care must also be taken to avoidexposure of those not involved in the operation such as local residents andbuilding occupants.

In a factory situation, the object to be coated can often be fully enclosedin a spray booth so that optimum ventilation can be applied to give excellentprotection to the operator. The reacting aerosols need to be removed from theexhaust air by filtration before the air is discharged to the outside atmosphere.A water curtain may also be used to remove overspray.

Some of the best designs of spray booth provide laminar airflow across theopening and allow operators freedom of movement whilst protecting them fromaerosols or spray droplets (Figure 2.37). All spray booths must be monitored atregular intervals to ensure that the enclosure and ventilation are fully effective.Ventilated enclosures are used, which protect those in the vicinity, when verylarge articles such as aircraft are sprayed inside a factory. Spray operators have


Rotatable pedestal

Exhaust

Water spray

1.0 m/saverage airflow

Airflow

Water torecirculation system

Figure 2.37 Water curtain spray booth. Figure reproduced with permissionfrom COSHH Essentials: Easy Steps to Control Chemicals, Health and SafetyExecutive, UK, 1999

to operate inside these areas and must wear full protective clothing includingpositive-pressure, air-supplied respirators.

There are less controllable spray operations, such as on-site rigid foam sprayinsulation. Typical operations include the spraying of industrial roofing, exter-nal storage tanks, building steelwork, and domestic roof spaces. Although someof these operations take place in a closed environment, adequate ventilation isoften not available because of the temporary nature of the operations. The onlysolution in all these cases is to use personal protection, including self-containedbreathing apparatus (Figure 2.38). Only personnel trained in the work, or underclose supervision, should be present.

Use of MDI and TDI in laboratories

Small-scale operations, such as quality control and formulation development,are carried out in laboratories. The handling of MDI and TDI in these situ-ations demands the same care and attention to the control of exposure as onpolyurethane manufacturing plants. Fume cupboards (hoods) with adequate airextraction rates need to be used for operations involving diisocyanates. If thelaboratory equipment will not fit inside a fume cupboard, then larger ventilatedenclosures will need to be provided. Personal protective equipment suitable tothe situation will be required. This will normally be safety glasses, a protectiveoverall or laboratory coat and impermeable gloves. All pouring, weighing andmeasuring of the diisocyanates should be carried out in well-ventilated fume


Figure 2.38 Hand-held spraying of rigid polyurethane foam

cupboards because open beakers or flasks provide situations for releases toair. The ‘tack-free’ times of rising foams should never be touch-tested unlessgloves are worn. Diisocyanates must never be pipetted by mouth. Current lab-oratory practice is to use syringes to measure diisocyanates volumetrically. Allspillages must be neutralized using the procedures already discussed in KeyTheme 3. Eating, drinking and smoking should not be permitted in laboratoryareas. Laboratory workers should receive routine medical surveillance in thesame way as production workers (Key Theme 2 ).

Visitors to the workplace

Most safety procedures are designed primarily for those present in the work-place on a regular basis. It is important to recognize that visitors who enterareas where diisocyanates are handled and processed should be included inthe safety system, as they may not know of the risks associated with over-exposure. Visitors will need to use the appropriate protective equipment, ofcourse, and should be accompanied at all times. One approach to protect vis-itors is to have them read and understand relevant safety information prior tosite entry. A possible text for recording that visitors have done this is shown.

INFORMATION FOR VISITORS TO DIISOCYANATE AREAS

MDI and TDI may cause adverse health effects, in particular respira-tory problems.

No visitors should enter a diisocyanate area if they suffer from bronchitis,bronchial asthma, repeated attacks of hay fever, or any other lung disease.


It is suggested that if any person is visiting the Company for more thana single day or on more than a single occasion, screening by medicalpersonnel should be considered.

Persons visiting the Company on a single occasion only, for a period ofone day or less, may be permitted to enter diisocyanate areas provided theyhave been informed of the potential risk and have assured the Companyrepresentative responsible that, to their knowledge, they do not suffer fromany of the above health problems.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Statement to be signed by the visitor

I have read and understood the above information.

To the best of my knowledge I do not suffer from any of the respiratorycomplaints detailed above.

NAME . . . . . . . . . . . . . . . . . . . . . . . . . . . (BLOCK CAPITALS)

SIGNATURE . . . . . . . . . . . . . . . . DATE . . . . . . . . . . . . . . . . .

Note to personnel accompanying visitors: it is important that one copyof this form be retained by the visitor and another be retained in Com-pany files.

Contractors and technical service personnel may visit sites using MDI andTDI on an intermittent basis only. They need special consideration since theirwork may lead them into over-exposure situations and they may be working inisolation. Consideration should be given to off-site and/or on-site training ofcontractors and technical service staff to ensure that they fully understand thehealth consequences of over-exposure. Long-term contractors should operatewithin the framework of a company’s safety system.

Emergencies in the workplace

All personnel must be capable of responding immediately to an emergencysituation. Emergency equipment should be available close to the work stationand should include machine stop buttons, and alarms, as well as personal pro-tection. The site needs to have emergency breathing equipment (self-containedequipment with compressed air cylinders or air line equipment and a suffi-cient provision of air line connections in the workplace). Eye-wash equipment,safety showers, a first aid box and decontamination equipment are required. Asemergency showers will be used very infrequently, their operation should bechecked at intervals. External showers, for example at unloading areas, shouldbe designed so that they do not freeze in cold conditions. Showers shouldprovide warm water (say at 20 ◦C) to prevent TDI solidifying if the water istoo cold. One or more of the staff in the location should be trained in first


aid techniques and should know how to summon professional help should thisever be required. All staff located in areas where diisocyanates are used shouldreceive training, and refresher training, on first aid procedure specific to diiso-cyanates. Further discussion of how to deal with emergency situations is to befound in Key Theme 6.

All the emergency procedures, including the use of the equipment, mustbe practised at intervals so that all staff know what to do should an emer-gency arise. A range of ‘routine’ emergencies may exist which have preplannedresponses. These need preparation and regular training by both workforce andmanagement. The first action in a developing emergency is to stop the processand make it safe, so that remedial action can be started. Once the process hasbeen stopped and emergency ventilation is operating then personnel have timeto assess the situation and prepare their next actions. The on-site emergencyresponse teams need to be able to call quickly for outside help (medical or firefighting services).

Similarly, the off-site emergency services should visit the site in advanceto familiarize themselves with the layout, location of the facilities and thehazards likely to be encountered. Regular practices, say annually, will oftenreveal or clarify weaknesses in the theoretical preparations. Typically, theyinclude issues of access, of the time delay before teams can be effectively onsite, and of communication.

It is important to liaise closely with the local community to advise localresidents of the nature of the operations, releases to atmosphere, and the impli-cations of an emergency, including any audible or visual alarms on the site.There may also be legal requirements for this information to be given to thelocal community. It is also useful to have prepared at least a general informa-tion and advice statement to distribute to the local community and the mediaif there is an incident.

Safety signs and posters

It is important to communicate safety instructions clearly, and these should bein the languages used by the workforce. Posters that provide useful reminderson the safe handling of MDI and TDI are available from suppliers and severaltrade associations. Pictorial signs may be valuable or even mandatory. Somesigns may be fixed; others will be portable for use in an emergency. Thefollowing examples may be useful.

Some examples of safety signs

NO SMOKING

WEAR RESPIRATORY PROTECTION

WEAR GLOVES

SAFETY GLASSES

FIRE FIGHTING EQUIPMENT

ESCAPE ROUTE


FIRE DOOR

EMERGENCY SHOWER

PROTECTIVE CLOTHING

SELF-CONTAINED BREATHING APPARATUS

EYE WASH

AIR LINE POINT

EMERGENCY STOP BUTTON

DO NOT ENTER: CONTAMINATED AREA

FIRST AID INSTRUCTIONS

DECONTAMINATION EQUIPMENT

ONLY AUTHORIZED EMPLOYEES AND VISITORS WEARING ANIDENTIFICATION BADGE ARE ALLOWED TO ENTER

Releases to atmosphere from polyurethane manufacturing sites

The vapour pressures of MDI and TDI are very low, and normal vapourreleases to atmosphere from polyurethane manufacturing sites are, typ-ically, at the parts per billion or parts per trillion level. There is littleevidence for any significant releases to atmosphere of diisocyanate aerosolsfrom polyurethane manufacture. Any coarse aerosols released from the pro-cesses will generally be deposited on exhaust ducting and react, probablyto form polyureas. Fine, gas-like aerosols may leave the exhaust stack, butare likely to evaporate during the dispersion of the releases.

Various abatement methods can be used to reduce airborne releases,notably carbon adsorption and water scrubbing. Carbon adsorption is highlyeffective in removing diisocyanates (and some co-released gases) fromexhaust ventilation air. However, it may be desirable to use an aqueousor other scrubbing method to capture certain other co-releases as wellas diisocyanate vapour, depending on the process and on local require-ments. Further, regulatory and practical aspects of destruction or cleaningof abatement media need to be considered in the choice of abatementmethod.

In this text the terms release and release to atmosphere have been used forlosses from the workplace into the external environment. Such releases areoften referred to as emissions, but this term is sometimes used by other authorsfor releases from equipment into the workplace. The term concentration exstack is sometimes used. This relates to the concentration of a chemical justbefore the exhaust stream emerges from the stack. The term fugitive emission


is commonly used only for losses of a chemical into the workplace, fromequipment, spillage, or leakage from equipment. Routine production releasesto atmosphere, usually at low concentrations, are sometimes referred to asnormal discharges.

Some authors use thelogical combination ofimmissions (into theworkplace) and emissions(out of the workplace),following German usage.

Only releases to atmosphere are dealt with in this text because releasing MDIor TDI into water or soil under normal operations is unacceptable. Depositionof MDI or TDI to water or soil in accidents within the factory site (thatis, within the fenceline) is unlikely to lead to releases beyond the fencelinebecause of the chemical and physical properties of MDI or TDI: such incidentsare covered in Part 4, The environment. Normal releases to atmosphere must beconsidered in terms of potential impact on the environment and on the healthof the community beyond the site, that is, beyond the fenceline. Such potentialimpacts are discussed in Part 5.6. This text concerns the sources of airbornereleases of MDI or TDI, techniques of abatement and typical concentrationsbefore and after abatement. Details of the methods of sampling and analysisof releases to atmosphere are given in Part 5.7.

Properties of MDI and TDI relevant to releasesto atmosphere

MDI and TDI have very low volatilities, and hence very low saturated vapourconcentrations (SVCs) at the temperatures used in polyurethane processing.The maximum concentrations of MDI and TDI as vapour at different air tem-peratures are given in Tables 5.4.6, 5.4.7 and 5.4.14. At 20 ◦C, the SVC ofpolymeric MDI is 0.03 mg/m3 and of TDI 100 mg/m3: these values apply toequilibrium conditions such as are found only in closed containers. Under thehighly nonequilibrium conditions of forced venting, their vapour concentra-tions are considerably lower than their SVCs, as will be illustrated. ModifiedMDIs or TDIs are even less volatile than their parent monomers, so will bereleased from polyurethane processes at even lower concentrations. MDI andTDI vapours adhere strongly to surfaces and there is evidence of adsorptiononto ventilation ducts. The high level of adsorptivity of MDI and TDI ontocarbon is very well established.

In some processes MDI, and possibly also TDI, may be released as aerosols:these may be reacting polyurethane mix aerosols or diisocyanate deposited ontoparticulates such as wood dust, for example from particle board production, orfine condensation aerosols of MDI. The aerosols formed from a reacting mix, orfrom diisocyanate deposited on natural products such as wood dust, are likelyto contain predominantly large particles and to be self-neutralizing, due to thepresence of polyols or water in the reacting mix and due to water in the naturalproducts, respectively. Such aerosols are likely to be deposited onto ventilationducting as a result of inevitable air turbulence in extraction systems. Only fine(gas-like) aerosols are likely to escape from the stack to the atmosphere. Vapourreleased from ventilation ducts will be broken down quickly to common airconstituents, due to hydroxyl radical attack in the atmosphere: the tropospherichalf-lives of MDI and TDI are of the order of 1 day. Accordingly, there is nolong-term cumulative MDI or TDI burden in the environment (see Part 4, Theenvironment).


Releases from polyurethane processesPolyurethane processes differ very considerably in the concentrations of diiso-cyanates emitted from the equipment. An important consideration is whetherthere is a need to install a forced air exhaust ventilation system in associa-tion with the given equipment. In some processes, the concentrations emittedinto the workplace may be well below occupational hygiene limits or evenundetectable. Decisions on the need for forced exhaust ventilation stacks toremove diisocyanates from the workplace will depend upon the concentrationsof diisocyanates and of other chemicals emitted from processes (co-releases),and upon local regulations. In some cases, particularly in MDI-based processes,the dilution ventilation (normal circulation and replacement of factory air) isadequate to fulfil regulatory requirements. In others, such as in flexible foamslabstock production using TDI, the use of forced exhaust ventilation (localventilation) is essential to maintain acceptably low workplace concentrationsof diisocyanates.

When required, measurements of concentrations should be taken in the duct-ing of the exhaust system, or near to the top of the stack, but not outside thestack because here the air volume flow rate cannot be measured. Clearly, mea-surements both in the primary ducting and close to the top of the stack areneeded to allow the effectiveness of abatement techniques to be assessed. Insome cases the stack will be fed from a plenum drawing air from a number ofprocessing units or work areas: in such cases it may be necessary to make a sur-vey of flow rates and mass balances under different process exhaust conditionsto allow meaningful diisocyanate release determinations to be made. It shouldbe noted that exhaust air in ducts may be moving at high speed, probablywith turbulent flow. If the diisocyanate is present as vapour only, the processof sampling of exhaust air is not critical and can be nonisokinetic. However,if the diisocyanate aerosols are not gaslike, sampling must be isokinetic (seePart 5.7, Sampling and analysis), otherwise results may be meaningless.

Forced ventilation is not usually feasible when the polyurethane processingis not within a factory or when very large objects are being sprayed. Examplesof such processes are the spraying of insulation on construction sites, thelaying of sports tracks and isocyanate-based paint spraying, including aircraftspraying. In these cases the impact of the operation on the environment andcommunity need to be assessed and precautions taken to reduce the risk to anacceptable level.

References on exposurefrom outdoor applicationsand spraying operationsPeterson et al. (1962);Fitzpatrick et al. (1964);Hosein and Farkas (1981);Bilan et al. (1989); Crespoand Galan (1999); Alcareseand Reisdorf (1999);England et al. (1999);Santolaya et al. (2000).

Over the past decade there has been a significant increase in interest inreleases from stacks, with a corresponding increase in the number of ex stackmeasurements taken of a wide range of chemical species, including MDI andTDI. Most of these release data have been generated on a single company orsingle site basis, with the results often submitted to regulators, but not pub-lished. To supplement this increased activity, and to allow the development ofa dialogue between industry and regulators regarding methodology and releaselevels, the International Isocyanate Institute Inc. (III) undertook a multi-partproject to characterize the releases from various types of MDI- or TDI-basedprocesses, and obtain a profile of the emissions situation in Europe. The projectfocused on those applications known to use the largest quantities of MDI andTDI, and the effect of abatement was studied. The study also included the mea-surement of co-releases associated with the given processes and the effect of


abatement media on their concentrations to allow a comprehensive approach toabatement. The same type of equipment was used throughout, as far as possible,and the studies were undertaken with rigour. For example, analytical equip-ment was calibrated with samples of the same materials as were used in thefactories being tested and, typically, this entailed up to 100 man hours of labo-ratory work prior to any given factory visit. Where information has been madeavailable, the results have been expressed in one of the following three ways:

1. Concentration of the releaseExample: 0.1 mg/m3 of TDI. The concentration is pertinent to potential res-piratory effects in the community. Concentration is used as a regulatorycriterion in the EU.

Example: 0.05 mg NCO group/m3. Concentration may also be expressed interms of total reactive isocyanate group (TRIG) concentration, a parame-ter used by some regulators. The TRIG concept is dealt with in detail inPart 5.6.

Example: 4 ppb TDI. The parameter used here is volume in volume. Thismeasure can be used only for vapour phase concentrations and not foraerosols. See Part 5.6.

2. Rate of mass releaseExample: 30 g MDI released per annum. Rate of mass loss is a startingpoint in considering the total environmental burden of diisocyanate. This isa criterion subject to regulatory scrutiny in the US.

3. Percentage of diisocyanate releasedExample: 5 mg MDI released per tonne of MDI processed. Percentage lossis a parameter to be considered in judging the efficiency of the combinedpolyurethane process and abatement system.

Releases from MDI-based processes (except flexible foam)Almost all rigid polyurethane foam is produced using polymeric MDI. Releasesfrom rigid foam processes vary considerably, depending upon the specifictechnology used. The lowest levels of releases arise from reaction injectionmoulding (RIM) techniques in which the mixing head is an integral part of themould, and the only escape of reacting MDI is from the mould breather holes.

Releases from rigid foam: slabstock and boardstock plantsIn the III series of studies on major MDI-using processes (Maddison andVangronsveld, 2000; Chapman, 2001) releases were measured in the stacksof five factories using two continuous processes: rigid foam slabstock andrigid foam boardstock (lamination) processes. The boardstock processes usedflexible facings. The results given in Table 2.11 record the MDI concentrationin the stack and the average annual percentage loss of MDI based on MDIthroughput, as calculated from the annual output of polyurethane.

The five plants were of different types, situated in five countries and whichused different chemical systems based on polymeric MDI. The concentrationsof MDI were measured using different analytical methods, which gave


Table 2.11 Summary of MDI releases from five different plants in Europe.

Process Stackconcentration

Annual MDImass release

Estimated PURannual output

MDI releasedas % of MDI used

µg/m3 g tonne million lb

Continuous boardstock (flexible facings)Plant 1 1.5 76 3000 6.6 4 × 10−6

Plant 2 1.3 8 6800 15.0 2 × 10−7

Plant 3 <0.4 <1 1200 2.7 <1 × 10−7

Continuous rigid foam blockPlant 4 3.7 23 3500 7.7 1 × 10−6

Plant 5 1.6 18 6000 13.2 6 × 10−7

Conversion factors: 1 g = 0.0022 lb; 1 tonne = 1000 kg = 2205 lb.For MDI vapour: 1 µg/m3 ≡ 0.096 ppb ≡ 0.34 µg/m3 NCO group.

extremely similar results on any given plant. The detection limit was about0.4 µg/m3.

The results showed that releases were at extremely low concentrations (<0.4to 3.7 µg/m3), such that abatement of these releases was not needed. Annuallosses from the plants were calculated as <1 to 76 g, and annual percent-age losses were 10−6 to <10−7 %, corresponding to an average of about 1 to10 mg/tonne MDI used in the continuous rigid foam block plants. One inter-esting aspect of the studies on boardstock machines was that all the isocyanatewas present as vapour in the releases from the liquid laydown of freshly mixedcomponents, whereas it was all present as particulate at the end of the linewhere the board was cut off. This indicated that the isocyanate group wasassociated with partially reacted MDI in the dust from the sawing operation.

Acton (2001) measured releases from a plant producing polyurethane pan-els with metal facings. Measurements were of concentrations of total reactiveisocyanate group (TRIG), VOCs, and toluene, specifically. Two stacks wereinvolved, these relating to releases from the reacting mix lay-down area, andto the panel saw-off area. In Table 2.12 are given the results as MDI concen-trations calculated from the TRIG concentrations reported. Concentrations ofMDI from the saw-off area were below the level of detection of the HPLCmethod used. No abatement was needed, even the higher releases from the lay-down area being very considerably lower than the maximum regulated releaseconcentration limit.

Table 2.12 Releases of MDI from a rigid-faced polyurethane panel plant.

From lay-down area From saw-off area

MDI stackconcentration


MDI releasedas % of MDI

MDI stackconcentration


MDI releasedas % of MDI

mg/m3 g used mg/m3 g used

0.038 300 4.0 × 10−5 <0.01 <10 <3.0 × 10−7

0.048 56 5.0 × 10−5 <0.01 <1 <3.0 × 10−7


Releases from fibreboard plantsMaddison and Merckx (1996) have reported on releases from medium den-sity fibreboard (MDF) plants based in three European countries. Fibreboard isproduced by coating wood fibres with polymeric MDI, then pressing and heat-ing them in a continuous process. Samples were taken from the exhaust air instacks from three different points in the fibreboard process. Table 2.13 gives thevalues recorded, as well as the local regulatory release limits, as then applied.The concentrations ex stack were so low that abatement was not needed.

Table 2.13 Releases from four fibreboard plants.

Exhaust air Plant 1 Plant 2 Plant 3 Plant 4from mg/m3 mg/m3 mg/m3 mg/m3

Dryer – 0.13 1.32 0.096Press 0.045 0.87 0.09 0.045Wet scrubber 0.072 – – –

Local limit 0.20 5.0 5.0 0.20

Releases from an oriented strand board plantOriented strand board (OSB) is produced by continuously coating natural fibreswith polymeric MDI, compressing the resulting product and steaming to curethe board. A study was made of MDI releases from the batch press vent of agiven process, this being the vent associated with the application and curingof the MDI. The study was of the concentrations in the vent, as measuredby two methods, the EPA Draft Method 207, which is very cumbersome, andthe OSHA Method 47. The following (Table 2.14) are the summarized results(Karoly, 2001, personal communication):

Table 2.14 Releases (unabated) from an OSB plant.

EPA Draft Method 207 mg/m3 OSHA Method 47 mg/m3

Range 0.16 to 0.38 Range 0.15 to 0.29

Releases from US sites using MDIA further programme of measurements and calculations was carried out bythe US Chemical Manufacturers Association, its successor organization, theAmerican Chemistry Council, the Alliance for the Polyurethanes Industry andthe USEPA. The aim of this programme was quite different from that of theabove studies, in that an attempt was made to estimate the maximum annualmass of MDI liberated to the atmosphere in the US, irrespective of ex stackconcentration or percentage loss of MDI during processing. This work wasto support a submission to the USEPA that there was no plausible case forlisting MDI as a High Priority Urban Air Toxic and to develop a more accurateNational Toxics Inventory for MDI (Price et al., 1998). Results taken from thatsurvey are given in Table 2.15. It should be emphasized that the values were


worst case calculations for sites releasing the maximum masses of MDI perannum for the cited applicational category. Thus, they should not be interpretedeither as typical, or as related to a single process. However, they are reproducedhere to give an insight into the order of maximum losses from US sites. Areview of the US situation regarding MDI releases from 1088 sites is given byRobert et al. (2001). Miller (2001) has reviewed measured MDI releases fromfoundries in the US.

Table 2.15 Estimated maximum annual releases of MDI from selected US sites.

Category Estimatedreleases

Category Estimatedreleases

kg/year lb/year kg/year lb/year

Air filter 3 7 Foam production 10 22Appliance 10 22 Foundry castings 6 13Appliance (truck) 2 5 Laminating 6 13Automotive 3 7 Mobile home products 4 10Boat building 0.5 1 Oil 0.5 1Coating (adhesive) 3 7 Packaging 3 7Coating (elastomers) 3 7 Rebonding 4 9Coating (sealant) 3 7 Recreation 3 7Coating (thermoplastic PUR) 3 7 Shoe soling 3 7Custom moulding 0.5 1 Fibres 3 7Door production 1 3 Specialty production 4 10Electronics 3 7 Tyre filling 1 3Filter devices 0.5 1 Water heaters 3 7

Releases of MDI and TDI from flexible foammoulding processesFlexible foam moulding is an operation whereby a polyurethane reacting mixbased on TDI, MDI or mixed MDI and TDI, or derivatives of them, is pouredor injected into a mould. The mould is opened when the foam has cured longenough to allow damage-free handling. In the traditional moulding systems(typically using TDI) the residence time in the mould is reduced by passingthe moulding through an oven: these are hot cure processes. With some sys-tems (typically using MDI) no oven is required: these are cold cure processes.In an III study in three European countries (Table 2.16) (Maddison and Van-gronsveld, 1996; Chapman, 2001) measurements were taken in the stacks offive flexible foam moulding lines manufacturing automotive seats. The stackswere not fitted with abatement equipment. The results of measurements in theabove study on other released species, such as catalysts and other chemicalsused in production, are given by Maddison and Vangronsveld (1996).

Releases from flexible foam slabstock production using TDIIn this process the reacting polyurethane liquid mixture is poured into a movingtrough in a tunnel which is equipped with exhaust ventilation. The mix-ture reacts to form a continuous block of foam, typically about 1 m × 2 m


Table 2.16 Summary of releases (unabated) from flexible foam moulding processes.

Factory Process Stack concentration Annual releaserate

Estimated PURannual output

Diisocyanate releasedas % of diisocyanate used

MDI TDI MDI TDI MDI TDImg/m3 mg/m3 g g tonne million lb % %

1 Car seatingcold cure <0.0001 0.019cold cure <0.0001 0.007

}26 1760 1400 3.1 2 × 10−5 6 × 10−4

cold cure 0.0005 0.004

2 Car seat mouldingcold cure 0.0125 – 794 – 420 0.9 6 × 10−4 –

Headrest mouldingcold cure 0.0009 – 75 – 250 0.6 9 × 10−5 –

3 Mouldingcold cure <0.0001 – <2 – – – – –hot cure – 0.5 – 13 620 510 1.1 – 9 × 10−3

}hot cure – 0.38

Conversion factors: MDI vapour,1 mg/m3 ≡ 0.096 ppm; 1 g = 0.0022 lb; 1 tonne = 1000 kg = 2205 lb;TDI vapour, 1 mg/m3 ≡ 0.14 ppm; 1 short ton (US) = 907 kg = 2000 lb.

cross-section. Lengths of block are sawn off and stored in a vented storagearea for about 1 day to allow the polymerization reaction to come to completionand for blocks to cool.

Over the past 20 years many programmes of work have been carried outto measure the concentration of TDI releases from flexible foam slabstockproduction. These have focused on concentrations in exhaust stacks, but somepractical studies have yielded information on environmental concentrations. Tuand Fetsch (1980) reported average levels from 3 to 8 mg/m3 (400 to 1100 ppb)from a range of 0.1 to 33.5 mg/m3 after a survey of stack concentrations ofa number of foam plants. Grey and Chadwick (1979) reported inlet concen-trations to an alkali scrubber between 300 and 670 ppb. The use of modernside and top paper technology on foam slabstock processes has been widelyadopted since some of the early measurements were made, and from morerecent measurements in the ducting of three plants, maxima around 300 ppbTDI are now common at air flow rates above 40 000 m3/h.

Some of the factors influencing TDI release concentrations are as follows:

Foam system variables: Processing factors:

• isocyanate index; • laydown conditions;• foam density; • edge papers;• cell opening characteristics. • top papers.

Plant design/geometry Ventilation air throughput

In Table 2.17 is given a summary of results obtained in III studies(Glover and Maddison, 1994; Vangronsveld and Maddison, 2002). The

values in this table were measured pre-abatement. The post-abatement valuesfor all factories are given in Table 2.28.

In Table 2.18 are given the rangesof concentration recorded by the citedauthors in the exhaust stacks offlexible foam slabstock plants, pre-abatement. The concentration results

are in a rather narrow range and are valuable in that regulators can makeestimates of levels of release, and from these estimate community exposure.


Table 2.17 TDI release concentrations (pre-abatement) from flexiblefoam slabstock machines.

Factory Foam type TDI concentration

mg/m3 ppb

1 Standard polyester 0.49 0.072 Standard polyether 5.9 0.832 High resilience polyether 1.9 0.273 Standard polyether 1.26 0.183 Combustion modified high resilience 0.15 0.024 Polyether, carbon dioxide blown 0.8 0.12

Table 2.18 Ranges of TDI emissions from flexible foam slabstock processes (pre-abatement).

Concentration Mass released per quantity ofTDI processed

Reference

ppm mg/m3 g/tonnea %

0.3 to 0.7 2 to 5 – – Grey and Chadwick (1979)0.4 to 1.1 3 to 8 50 5 × 10−3 Tu and Fetsch (1980)

0.02 to 0.85 0.15 to 5.9 25 2.5 × 10−3 III studies: Table 2.170.2 to 0.5 1 to 4 – – Palfy (2000/2001)

Conversion factors: 1 tonne = 1000 kg = 2205 lb; 1 g = 0.0022 lb; 1 short ton (US) = 907 kg = 2000 lb.aFor comparison, the losses of MDI from rigid foam slabstock were in the range of 1 to 10 mg/tonne. See Table 2.11.

However, the concentration results should be considered with some caution.Firstly, they are highly dependent upon air flow rate and ducting arrangements,and these are specific to a given situation. Secondly, they depend upon thespecific production process used. In summary, concentration is specific to siteand process and ‘typical’ or average values cannot be obtained from Table 2.18.A specific situation can be characterized only by direct measurement ofconcentration.

Metcalf and Sweet (1993) attempted to devise a formula to calculate theconcentrations of releases from flexible foam slabstock plants. The formulawas derived from the results of measurements on several US plants, and gavea good statistical fit. However, when the results from the III studies cited abovewere applied, the formula gave the correct value in only one case. The formulais probably applicable only to processes which are very similar to those usedto derive the formula.

TDI isomer ratios in releases from flexible foam slabstock processesIt has been well established that TDI isomer ratios change during polyurethaneReferences to change in

isomer ratio duringpolyurethane processingGrey and Chadwick (1979);Nutt et al. (1979); Randoand Hammad (1985);Tinneberg et al. (1997).

flexible foam processing. The airborne TDI released from the process is richerin 2,6-TDI than is the original TDI (Nutt et al., 1979). This is mainly attrib-utable to the faster rate of reaction of the 2,4-TDI isomer with the reactionmix. It has also been shown that the percentage of 2,6-TDI in the air abovea flexible foam line increased along the line, as compared with 2,4-TDI. In


Table 2.19 are given ratios calculated from the results of measurements ofindividual TDI isomers in flexible foam slabstock and moulding operations:

Table 2.19 Change in TDI isomer ratio from that in the original 80/20 TDI.

Plant Type of foam 2,4-TDI in rawmaterial

2,4-TDI in TDI inexhaust stream

% %

Slabstock production

1a Standard polyester (TDI) 80 272a Standard polyether (TDI) 80 203b Standard polyether (TDI) 80 394b Standard polyether (TDI) 80 415b Standard polyether (TDI) 80 476a Fire retarded high modulus (TDI) 80 267a Combustion modified (TDI) 80 328c Polyether, carbon dioxide blown 80 19

Moulding productiond

8 Cold cure (MDI/TDI) 80 509 Cold cure (MDI/TDI) 80 21

10 Hot cure (TDI) 80 3311 Hot cure (TDI) 80 37

aGlover and Maddison (1994).bNutt et al. (1979).cVangronsveld (2001).dMaddison and Vangronsveld (1996).

Releases from flame lamination processesFlame lamination is a technique whereby a thin layer of polyurethane flexiblefoam is combined with a textile or textiles to produce a fabric with differentproperties. The process involves heating a continuous thin layer of polyesteror polyether foam with a bank of flames. The melted surface of the foam isself-adhesive and bonds to the textile in the combining process. The exhauststack gases comprise low concentrations of diisocyanates and combustion gasessuch as carbon monoxide, carbon dioxide and nitrogen-based compounds. InTable 2.20 are given the results of measurements taken of diisocyanates in thegases in the stack (Glover and Maddison, 2000) prior to carbon abatement.Their report also gives information on the concentrations of other chemicalsin the exhaust stream, before and after abatement: data on the abatement ofTDI are given in Table 2.28.

Releases from hot-wire cutting of flexible foamIn Table 2.21 are given the concentrations of TDI measured by Nutt (1982)in the exhaust gases from hot wire cutting of fire-retarded polyether slabstockfoam. The HPLC traces indicated that a diversity of isocyanate-ended speciesmight also be present. Interestingly, the change of isomer ratio of the TDI


Table 2.20 Stack concentrations of diisocyanates from flexible foamflame lamination processes (pre-abatement).

Foam type Diisocyanate concentration mg/m3

2,4-TDI 2,6-TDI 4,4′-MDI

Standard polyester foam (TDI) 0.30 0.05 –Standard polyether foam (TDI) 2.00 0.22 –Standard polyether foam (MDI) – – 0.048

Conversion factors: MDI vapour, 1 mg/m3 ≡ 0.096 ppm;TDI vapour, 1 mg/m3 ≡ 0.14 ppm.

Table 2.21 Concentrations of TDI in hot wire cutting exhaust gases.

Test 2,4-TDI 2,6-TDI TDI total 2,4-TDI in TDI inexhaust stream

mg/m3 mg/m3 mg/m3 %

1 1.0 2.9 3.9 262 1.1 2.2 3.3 333 2.1 3.7 5.8 36

Conversion factor: TDI vapour, 1 mg/m3 ≡ 0.14 ppm.

from that of 80 % 2,4-TDI in the original material to those in the exhaust airsamples indicates preferential thermolysis of the polyurethane bond formedfrom the polyol and 2,6-TDI. Whilst the precision of these figures is lowerthan those normally achieved in recent studies, and the results represent onlyone scenario, the broad indications of this work are useful, given that hot wirecutting is still used.

Releases of MDI and TDI from prepolymerand manufacturing elastomer processesMDI releases from the production of an MDI prepolymer, and its use in elas-tomer manufacture have been studied (III unpublished data). Measurementswere taken (1) during charging of the prepolymer reaction vessel and (2) fromthe reaction vessel for producing about 10 tonne of prepolymer. The prepolymerwas used for producing elastomer shoe soles by (3) dispensing the prepoly-mer/polyol blend from a mixing head into moulds. Subsequently, the soles

Table 2.22 Prepolymer and shoe sole manufacture: MDI release concentrations.

(1) Charging (2) Prepolymermanufacture

(3) Moulding (4) Degreasing

µg/m3 µg/m3 µg/m3 µg/m3

<1 <1 <1 <1

Detection limit: 1 µg/m3 for MDI.


were (4) degreased and finished. The results are given in Table 2.22. A limitedsurvey of a few elastomer production units suggests that releases of MDI andTDI are very low, that is, of the order of 0.3 µg/m3 or even lower (Hurd, 1995,personal communication).

Volatile organic compounds

VOCs have become an issue within the context of global warming.Destruction of the ozone layer is believed to be a function ofboth type and concentration of certain VOCs. Definitions of VOCsdiffer very significantly according to regulatory authority and thesedefinitions are not scientifically compatible. TDI, and especially MDI,might be considered by the scientist as involatile organic compounds(see Tables 5.4.7 and 5.4.14). However, both MDI and TDI werelisted as VOCs within the terms of the USEPA definition (USEPA,1994) which is: VOC means any compound of carbon, excluding CO,CO2, H2CO3, metallic carbides or carbonates, and (NH4)2CO3, thatparticipates in atmospheric photochemical reactions. Certain solventsare exempted because of their photochemical reactivity. The EuropeanUnion definition, based on volatility, excludes MDI and TDI.

Releases of compounds other than MDI or TDI frompolyurethane processesAlthough this text is concerned primarily with MDI and TDI, releases ofother chemicals present in polyurethane processing need to be considered,in order to assess what method or methods of abatement are appropriate,if any. Chemicals which are co-released include auxiliary chemicals used

in polyurethane processes, such ascatalysts, blowing agents, antioxidantsand solvents present in some rawmaterials, as well as solvents frommould release agents or from solventflushing of mixing heads. It may benecessary to consider such chemicalswithin regulations on volatile organiccompounds (VOCs), as well as onspecific species.

For instance, in the screening testsfor the research project discussedlater, the following compounds weremeasured in the releases from thestack of a flexible foam slabstock

process (Maddison and Vangronsveld, 1996):

• methylene chloride;• silicone carrier solvents;• toluene;• tertiary amine catalysts.

The same research programme has given valuable quantitative data on suchsubstances released from several types of polyurethane production. These datawill allow an assessment of the risks that the substances may constitute andwhat effective technical and economic abatement technology it may be neces-sary to consider.

Tertiary amine catalystsGas chromatography with mass spectrometry has been used to measure the con-centrations of some typical tertiary amine catalysts released from polyurethaneprocesses producing several types of polyether and polyester flexible foamslabstock and mouldings. The total concentration determined in the releaseswas not more than 1 ppm from each of the three polyether foam productionplants and 6.5 ppm from a polyester foam production line. The data suggestthat a minor percentage of the tertiary amine catalyst used in the reaction mixis emitted in the foam conveyor section of the process, the rest being lostin cure and storage areas, or retained in the foam. Catalyst manufacturers are


offering wider ranges of reactive catalysts, and polyol-grafted catalysts, furtherto reduce releases to atmosphere.

Blowing agentsBlowing agents currently used in polyurethane technology include liquid car-bon dioxide, isopentane, cyclopentane, butane, propane, acetone and the fluo-rocarbons containing hydrogen, such as HCFC 141B, HFC 152A, HFC 134Aand HFC 245FA. A number of analyses of the release concentrations of CFC-11, a chlorofluorocarbon, and methylene chloride, both of which were usedvery widely in flexible foam processes, have been reported, as have assess-ments of the percentage recovery of the CFC-11 by the use of activatedcarbon beds (Sporon-Fiedler, 1986; Nutt and Skidmore, 1987). Although thesetwo substances are being phased out as blowing agents, the results are use-ful in understanding releases of other blowing agents in what is essentiallyan unchanged process. The concentrations in releases of the blowing agentmethylene chloride have been measured and pre-abatement concentrations upto 24 g/m3 have been found, similar to the levels of CFC-11 reported. Withboth CFC-11 and methylene chloride, approximately 50 % of the total used isemitted in the conveyor section of the flexible slabstock process.

Abatement of releases

Criteria for abatementThere was little regulatory interest in releases of MDI or TDI until the mid1990s. This was primarily because of the low levels of releases: also, therehad been little regulatory activity associated with chemicals, in general. Fur-ther, it had been well established (Part 4, The environment ) that MDI and TDIhave little environmental impact and that they decay in air. However, severalregulatory authorities have now established ex stack maximum release concen-trations for these materials. Further, in the US there are fenceline (community)maximum concentrations for MDI and TDI, within the IRIS programme ofestablishing community risk from releases of chemicals.

Ex stack concentrations are relatively easy to determine, using well-established methods. Fenceline compliance measurements are more complex:they involve direct measurements at the limits of analytical methodology(typically 1 to 100 parts per trillion), or the use of modelling of ex stackconcentrations. Modelling involves the use of meteorological conditions at thesite, factory site parameters and geographical features of the surrounding area.These topics are discussed in Parts 4 and 5.6.

Abatement methodsSeveral methods have been investigated to reduce releases of MDI or TDIpresent in the exhaust air of ventilation stacks. Of the methods tested, onlyneutral and alkali aqueous scrubbing and carbon adsorption methods haveproved to be both practically and economically viable. The choice of methoddepends upon the co-releases of chemicals which also have to be abated. Pilotstudies have been carried out on the destruction of releases using OH radicalsor biological media but these have not led to commercial development of


the methods, probably due to the simplicity and effectiveness of carbon oraqueous systems.

Activated carbon adsorption systemsDesign of activated carbon unitsA wide range of designs has been tested, and selected ones used commercially,over the past 25 years. The carbon has been used as plates or in granular form.Whilst carbon in the plate form avoids the problem of air channels forming,the problems of sealing the plates in the exhaust ducting have been found tobe significant. Carbon, as granules, has been used in systems with multiplelayers, or as a single large bank. A problem with multiple layers is to preventextensive channelling (and hence short contact time of the carbon with theexhaust gases) at each layer. Modern systems use large banks of granularcarbon either in a cylinder or in an annular configuration (see Figure 2.39).

Inlet connection

Filling port with cover

Outer screen

Carbon media

Inner screen

Outlet connection(to exhaust fan)

Typical plan view showing flanged inletconnection and filling covers overperforated annular screens

Typical section showing bed of activated carbonretained between perforated annular screens.

Figure 2.39 Diagram of the operation of an annular carbon bed abatement unit. Reproduced by kind permis-sion of Camfil, Blackburn, UK


There are five critical aspects to be considered:

• contact time of MDI or TDI with the carbon;• type of carbon;• channelling in the carbon bed;• clogging of the carbon bed;• blocking of the carbon by debris.

The contact time of the exhaust air with the carbon is defined as the velocityof air flow through the bed divided by the bed thickness: for example, a linearvelocity of 0.4 m/s (1.3 ft/s) and a bed thickness of 1 m (3.3 ft) would give acontact time of 2.5 s. Control of linear velocity, and hence residence time, ofthe exhaust gases in the adsorption unit is critical. For effective TDI removalone manufacturer has recommended that the air velocity should not exceed0.5 m/s (1.6 ft/s) and that the contact time should be at least 2 s. Adsorbersusing these criteria have operated successfully for over 15 years, reducing TDIemissions to acceptable discharge concentrations.

Since beds may use several tonnes of carbon and last for years, the choice ofcarbon type is critical. It is important that experts be consulted and, if neces-sary, small-scale laboratory tests carried out. It is not difficult to calculate therequired contact time. However, in that respect it should not be assumed thatthere is even flow through the carbon. Channelling in the carbon bed, whichresults in air passing preferentially through open channels formed mechanicallyin the carbon bed, leads to reduced contact time of the exhaust gases with thecarbon, and hence to lower adsorption efficiency. Clogging of the carbon bed,where carbon particles adhere to each other at the inlet of the bed to form amass of low permeability, can also be a problem: the pressure across the bedbecomes so high that exhaust gases cannot be forced through it. Mechanicalbreak-up of the carbon at the inlet end of the bed may be necessary to preventthis. An associated phenomenon is blocking of the carbon by dust and otherdebris. Some manufacturers use a so-called sacrifice layer before the carbonadsorption unit. This is a unit containing cut scrap flexible polyurethane foamor other removable material. This has the function of reducing channellingof the air by preventing any debris from the air collecting at the inlet of thecarbon adsorption unit. Further, it is well known that flexible foam adsorbsdiisocyanates very strongly, so the concentration of diisocyanate entering thecarbon adsorption unit is already reduced. The sacrifice layer is replaced veryfrequently at low cost. This use of flexible foam for the abatement of diiso-cyanate has been described (Wood et al., 1993).

The concentration of TDI decreases as the air passes along ducting to thecarbon bed, due to adsorption on the side walls. One company using a sub-stantial length of ducting found a reduction of 30 to 40 % of the initial TDIconcentration. Thus, when measuring the efficiency of a scrubber unit the inletconcentration should be measured near to the entrance of the scrubber.

In Figures 2.40 and 2.41 are illustrated carbon adsorption units for flexi-ble foam slabstock releases, and flame lamination releases, respectively. Therehas been considerable experience with such carbon beds, some of which isdescribed below. In one case, the carbon bed was changed after 7 years ofoperation, not because of loss of efficiency (still >99 %), but because of theincrease in back pressure. The use of a simple acrylic filter impregnated with


Figure 2.40 Carbon abatement unit for emissions from flexible polyurethanefoam processing. Reproduced by kind permission of Camfil, Blackburn, UK

Figure 2.41 Carbon abatement unit for emissions from a polyurethane flamelamination process. Reproduced by kind permission of Camfil, Blackburn, UK


activated carbon before the main carbon bed, not only removed particulates, butalso reduced the concentration of TDI by approximately 20 %. The acrylic filterneeded to be renewed frequently. In another case, the carbon bed was reportedas freezing at very low ambient temperatures and it consequently failed to oper-ate until heated by warm air. In Table 2.23 are given the results of analysis ofthe same type of carbon used in three different carbon adsorbers over a periodof 7 years (III unpublished data). It had already been ascertained that the max-imum loading of the given carbon was about 25 g per 100 g reaction productcalculated as TDI product. It can be seen that there was a gradation of loadingfrom the inlet to the outlet in all three adsorbers. In Adsorber 1 the saturationloading (25.4 g per 100 g carbon) had been reached and the remaining lifetimeof this adsorber was very limited because of the reducing carbon contact time:in the cases of Adsorbers 2 and 3 there was still considerable capacity, thisbeing due to the lower concentrations of TDI being passed through them.

Table 2.23 Loadings of TDI/reaction product on carbon adsorbers.

Position in bed TDI/reaction product loading on carbon g/100 g

Adsorber 1 Adsorber 2 Adsorber 3

Exhaust gas entry 25.4 22.8 24.0Middle 22.3 7.3 6.0Exhaust gas exit 11.8 5.1 4.1

Note: saturation loading by TDI is about 25 g per 100 g carbon.

Analysis of used carbonSamples of activated carbon from the above three carbon adsorbers were exam-ined. The spent carbon was grey in colour. Analysis of this spent carbonshowed that neither TDI nor TDA were detectable (detection limit: 5 mg/kg)so that any nitrogen present would probably be as polyureas. The results ofchemical analysis are given in Table 2.24, where the figures are expressed aspercentages of the carbon in the bed (w/w). In addition to the results of analy-sis are given calculated values of the percentage of polyurea which would beformed if all the nitrogen were converted to polyurea: the value approachesthat of 25 g per 100 g carbon given in Table 2.23.

Table 2.24 Analysis of carbon from beds.

Bed Extractable nitrogen TDI TDA Fixed nitrogen

% % % % % as ureaa

1 nd nd nd 4.0 212 nd nd nd 3.2 173 0.06 nd nd 3.2 17

nd = not detected (detection limit 5 mg/kg).aCalculated.


Reactivation of activated carbonThe above carbon was reactivated by heating in a process used by the originalsupplier. The results of reactivation tests showed that the grey colour and poly-merization products could be totally removed along with the adsorbed impu-rities. The reactivated product was found to have good adsorption capacity, asmeasured by benzene adsorption, which is used as a standard. It was concludedthat the spent carbon could be reactivated and re-used in air purificationapplications.

Aqueous scrubbingAqueous alkali scrubbing of MDI and TDI has been used with success in theUK for more than 20 years. Typical systems use a bed packed with polypropy-lene spheres to provide a large surface area for the scrubbing agent, sodiumhydroxide solution. The alkali trickles through the bed under gravity, the extractair is forced upwards and permeates the bed, and the diisocyanate is removed byreaction with the alkali. The alkali is recirculated. Grey and Chadwick (1979)published details of the design of the Cleme Gas Scrubber, and reported thata conventional twin impingement plate scrubber unit gave only approximately50 % efficiency. Modifications were carried out to the design and eventuallyan efficiency of greater than 90 % was achieved. It should be noted that theconcentration of diisocyanate in the gas phase before abatement is so low thatthere is negligible change of the temperature in the aqueous scrubber due tothe heat of reaction.

Grey and Chadwick reported that the first unit installed made no provision foreasily monitoring and adjusting the strength of the sodium hydroxide scrubbingliquor. As a result of the removal of carbon dioxide from the exhaust ventilationgas stream, sodium hydroxide became progressively consumed and convertedthrough sodium carbonate to sodium bicarbonate. The scrubbing action of 0.3to 5 % sodium carbonate solution was known to be as efficient as 0.25 to4 % sodium hydroxide, but sodium bicarbonate was less effective. Steps weretaken to improve the control of alkalinity of the scrubbing medium using anautomatic dosing system, which replenished the sodium hydroxide level byinjecting 30 % aqueous sodium hydroxide through appropriate valving andpumps. Other designs of aqueous scrubber have been developed. One foammanufacturer evaluated a packed tower design. The work indicated that anefficiency of greater than 95 % using alkali scrubbing could be guaranteed.Efficiencies of the order of only 80 % were achieved when water rather thanaqueous alkali was used as the scrubber liquor. A possible improvement to thisproblem was used by one foam manufacturer, who found that the replacementof alkali by aqueous solutions of urea gave scrubbing efficiencies close to thoseobtained with alkali, and significantly higher than those with water.

An improvement over water scrubbing might be to combine it withaqueous oxidation. It is already known that MDI and TDI are oxidizedby hydroxyl radicals which could be generated in the aqueous system.Pilot trials have indicated that such a system would be viable (Barkerand Jones, 1988)

Neutral aqueous scrubbing can beachieved by the use of venturi systems.Hurd (1988) has described the useof single-stage and multi-stage venturiinstallations on two UK flexible foamslabstock plants. A single venturi

installation on one plant operating at approximately 50 000 ft3/min of airgave about 50 % efficiency with inlet TDI concentrations of around 1000 ppb.


Very good results have been obtained, however, using three venturi scrubbersin series. This plant operated with an air extraction rate of 64 000 ft3/min(115 200 m3/h) of air. The inlet TDI concentration was monitored continuouslyby a paper tape monitor. The data from the monitor were fed to amicroprocessor. Automatically, the number of venturis required to reducethe outlet TDI concentration to below 20 ppb were brought into operation,assuming 55 % efficiency in each successive venturi jet in the series ofthree jets. The full series of three were required only when particular foamformulations leading to higher levels of TDI emissions were being run. Amaximum scrubbing efficiency of not less than 90 % was obtained with allthe venturis in operation. Water usage was high, however, so a recirculationsystem was established.

Effluent from aqueous scrubbersThere are widespread regulations regarding the release of aqueous factorywaste into water systems. In order to conform to acceptable standards a knowl-edge of the composition of the scrubbing liquors, and the local criteria fordilution and disposal, are essential. The effluent waters from two polyurethanefactories releasing effluents into water systems were analysed within an IIIprogramme (Chapman, 2001).

One of the factories used a water scrubber, whereas the other factory em-ployed an alkali scrubber. TDI could not be detected in either effluent. How-ever, low levels of its reaction product, toluene diamine (TDA), were foundin both. TDA is expected to be easily removed from the effluent by a watertreatment plant since it is very strongly adsorbed onto the activated sludge(Cowen et al., 1998). Measurements of Total Organic Carbon (TOC), Dis-solved Organic Carbon (DOC) and Chemical Oxygen Demand (COD), alongwith concentrations of various chemical species were reported. The overallconclusion was that upon natural dilution of the effluent, it would have similarcharacteristics to those of water from public treatment plants. Solids formedin the neutralization process, and removed from the above aqueous effluent,should be disposed of in conformity to local regulations. Whilst there has beena general trend to use carbon abatement rather than the less efficient aqueoussystems, interest in aqueous systems continues (Griggs et al., 2000).

Efficiencies of TDI abatement: pilot studiesUrano at Yokohama National University (1978) carried out work on the use ofactivated carbon to adsorb TDI. He reported that an adsorption capacity of 0.3to 0.5 g TDI/g carbon would be achievable even at low concentrations of TDIin air. These values should be viewed in the light of those given in Table 2.23.A very high adsorption rate for CFC-11 (which was then used universally as ablowing agent) was also reported. He also reported that for triethylenediamine(TEDA), a widely used polyurethane catalyst, the adsorption capacity of thecarbon was large, but the adsorption rate was low (this may have been due toadsorbed TEDA being lost from the carbon to the exhaust stream). An impor-tant contribution to the data on the use of activated carbon for TDI removal andCFC recovery was made by Gans et al. (1983) and by Sporon-Fiedler (1986).

References oncarbon abatementUrano (1978, 1979); Ganset al. (1983); Urano andYamamoto (1984);Sporon-Fiedler (1986); Nuttand Skidmore (1987).

Gans and his co-workers at Stuttgart University carried out a detailed inves-tigation of the removal of TDI and CFC recovery from polyurethane emissions,


both on the laboratory scale and on a large scale pilot plant, in collaborationwith industry. Further, more detailed analytical tests on this pilot plant werereported by Nutt and Skidmore. They reported that the unit was >99 % efficientfor TDI removal and that CFC-11 recovery was also viable.

Efficiency of TDI abatement: large scale experience using activatedcarbon unitsFollowing the pilot scale tests reported above, a number of carbon adsorberswere installed on flexible polyurethane foam plants, notably in the UK, Hollandand Belgium. Data are now available from these units in terms of efficiency,life and the cost per tonne of TDI treated. Two units which had been operatingfor over 7 years showed no detectable TDI at the exit from the scrubbers. It hasbeen found that a reduction in the air volumes used in polyurethane flexiblefoam slabstock production was necessary to obtain efficient and economicabatement methods, since capital costs, running costs and space requirementof abatement equipment all increase substantially with increased air volume.Costs will also of course be dependent upon plant output, space requirementsand other factors. Substantial reductions of air volumes can be achieved by astudy of operating and ventilation conditions. One company, when installingcarbon adsorption units, reduced exhaust volumes on a flexible foam slabstockline from approximately 80 000 to 45 000 m3/h using extraction above the sidewall instead of the conventional overhead exhaust. In spite of this change,concentrations of TDI in the workplace did not increase.

The results from a later research programme confirmed the efficiency ofactivated carbon units for TDI removal (see Table 2.25 for example). Runningcosts vary depending on the variables outlined but, as a general guide, are ofthe order of US $2.5 per tonne of TDI processed by the factory (2001).

Table 2.25 The efficiency of carbon bed abatement of TDI from flexible foam production.

Foam type TDI concentrationbefore abatement

TDI concentrationafter abatement

Efficiency

mg/m3 mg/m3 %

Polyester 0.246 0.0058 98Polyether standard 2.95 nda (<0.001) approx. 100Combustion modified polyether 0.794 nd (<0.001) approx. 100

Conversion factor: TDI vapour, 1 mg/m3 ≡ 0.48 mg/m3 NCO group ≡ 0.14 ppm.and = not detected.

Abatement of releases from flame laminationIn Table 2.26 are given the effects on concentrations of MDI and TDI releasesfrom flame lamination of MDI-based and TDI-based polyurethane foams ofusing carbon abatement (Glover and Maddison, 2000). All concentrations ofMDI or TDI, post-abatement, were below any regulatory maximum require-ment, and below the detection limits of the method, which were 0.03 mg/m3

for MDI and 0.02 mg/m3 for TDI.The authors also reported on the abatement of carbon dioxide, carbon monox-

ide, nitrogen oxides, hydrochloric acid and hydrocyanic acid from the exhaust


Table 2.26 The abatement of MDI and TDI from flame lamination processes.

Foam type Releasedspecies

Concentrationpre-abatement

Concentrationpost-abatement

Efficiencyof abatement

mg/m3 mg/m3 %

Polyester (TDI) 2,4-TDI 0.31 <0.02 >942,6-TDI 0.53 <0.02 >96

Polyether (TDI) 2,4-TDI 2.12 <0.02 >992,6-TDI 0.24 <0.02 >90

Polyether (MDI) MDI 0.05 <0.03 nma

anm = statistically not meaningful to calculate this value.

stream. In most cases gases were reduced to, or near to, the level of theanalytical detection limits. This work was carried out using new carbon, sothe above values reflect optimal abatement for that plant. However, since thatstudy was completed (in 1993) there have been significant developments in thetreatment of carbon to adsorb specified chemicals such as hydrochloric acid,hydrocyanic acid and amines, in the last case using acid-treated carbon.

Abatement of blowing agents, amine catalystsand other speciesIt is beyond the scope of this text to deal with the abatement of species otherthan MDI and TDI. Furthermore, individual abatement scenarios need to beexamined to allow meaningful approaches to co-abatement to be made. Thecitations provided below give a considerable amount of information aboutthe concentrations of chemical species which may be released from MDI- orTDI-based processes.

References to studies about diisocyanate co-releasesIn these reported studies, co-releases were determined, in most cases beforeand after abatement.

Flexible foam slabstockGlover and Maddison (1994)VOCs, methylene chloride, toluene, amine catalysts, metal catalysts, organ-ophosphorus, halogens, substituted phenols, other.

Vangronsveld (2001)Fire retardants, blowing agents, glycols, aliphatic amine catalysts, VOCs.

Flexible foam mouldingMaddison and Vangronsveld (1996) and Chapman (2001)VOCs and tertiary aliphatic amines.

Flame laminationGlover and Maddison (2000)Carbon monoxide, carbon dioxide, hydrocyanic acid, hydrogen chloride, nitro-gen oxides (NOx), aromatic amines, VOCs, acid gases.


Rigid foam slabstock and boardstockMaddison and Vangronsveld (2000)Amine catalysts, fire retardants, glycols, blowing agents and flushing agents.Acton (2001)VOCs and toluene.

MDI and TDI: summary of release and abatement dataIn Table 2.27 are summarized the data detailed in previous tables.

Table 2.27 Summary of pre-abatement releases.

Application Concentration Annual loss Release Release based onestimated annual

usage of diisocyanatemg/m3 g g/tonne %

MDIRigid foam block 2 to 4 × 10−3 20 to 25 (3 to 7) × 10−3 (6 to 10) × 10−7

Boardstock (flexible facings) (<0.4 to 1.5) × 10−3 <1 to 76 (<8 to 250) × 10−4 –Boardstock (rigid facings) <0.01 to 0.05 <10 to 300 (<2 to 350) × 10−3 (<3.0 to 500) × 10−7

Fibreboard 0.05 to 1.3 – – –Oriented strand board 0.2 to 0.4 – – –Flexible foam moulding (0.1 to 10) × 10−3 <2 to 26 (2 to 200) × 10−2 (2 to 60) × 10−5

Flame lamination 48 × 10−3 – – –Prepolymer manufacture <10 × 10−3 – – –Shoe-sole manufacture <10 × 10−3 – – –Elastomers 3 × 10−3 – – –

TDIFlexible foam slabstocka 0.2 to 8 – 25 to 50 (2.5 to 5.0) × 10−3

Flexible foam moulding 0.004 to 0.5 (1.8 to 14) × 103 1 to 28 (0.6 to 9) × 10−3

Flame lamination 0.05 to 2 – – –Hot-wire cutting 4 to 6 – – –Elastomers 3 × 10−3 – – –

Conversion factors: for vapour, MDI 1 mg/m3 ≡ 0.096 ppm; TDI 1 mg/m3 ≡ 0.14 ppm.Saturated vapour concentrations (50 ◦C): polymeric MDI 1 to 2 × 10−2 µg/m3; TDI 1.2 × 106 µg/m3.aResults of Tu and Fetsch (1980), Chapman (2001) and Maddison and Vangronsveld (2000) (Table 2.18), combined.

In Table 2.28 are given data collected on the abatement of TDI emissions.There are no MDI abatement data available because the unabated releases werelower or much lower than the prevailing regulatory limits.

The values given in Table 2.27 are drawn from the studies cited in previoussections of the text. The ranges of results are probably representative of theglobal scene, given that the studies were of the applications consuming mostof the MDI and TDI used worldwide, and given that the same proprietarymanufacturing processes for these applications are found worldwide.

The key parameter is mass loss of diisocyanate per mass of diisocyanate pro-cessed, based on a per annum calculation, whether as g/tonne or % diisocyanatelost. Ex stack concentration is a less fundamental parameter, being inverselyproportional to the volume flow of exhaust ventilation air, to an approxima-tion. Releases of MDI range from <6 × 10−7 % to 6 × 10−4 % of total MDI


Table 2.28 Summary of TDI abatement data.

Application Pre-abatementconcentration

Post-abatementconcentration

Abatement Notes

mg/m3 mg/m3 %

Flexible foamslabstock

From Table 2.25

Polyether foam 0.8 to 3.0 <0.001 ca 100Polyester foam 0.25 0.006 98

Flamelamination

From Table 2.26

Polyether foam 0.25 to 2.1 <0.02 90 to 99Polyester foam 0.42 <0.02 >94 to >96

throughput, which equate to a range of <0.8 mg/tonne to 2 g/tonne, in the veryhigh volume rigid boardstock and rigid foam slabstock sectors. Losses of TDIrange from 2.5 × 10−3 % to 9 × 10−3 %, which equate to the range of 1 to90 g/tonne TDI, for the dominant TDI usage sectors of flexible foam slabstockand moulding.

The unabated concentration and annual loss values for MDI were extremelylow, and below all ex stack limits which applied, the most stringent of whichwas (and still is in 2002) 0.1 mg NCO group/m3 (equivalent to 0.3 mg MDI/m3)as required by the UK Environment Agency. Accordingly, the values calcu-lated for the efficiency of abatement (Table 2.28) relate to TDI or TDI-basedpolyurethane (flame lamination) only.

Reading

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Further reading

Gum, W. F., Riese, W. and Ulrich, H. (1992). Reaction Polymers: Polyurethanes, Epoxies, UnsaturatedPolyesters, Phenolics, Special Monomers and Additives; Chemistry, Technology, Applications, Markets,Carl Hanser, Munich (ISBN 3-446-15690-9).

Oertel, G. (1983). Kunststoff Handbuch 7: Polyurethane, 2nd edn. Carl Hanser Verlag, Munich (ISBN3-446-13614-2).


Oertel, G. (1993). Polyurethane Handbook: Chemistry–Raw Materials–Processing–Application–Proper-ties, 2nd edn. Carl Hanser Verlag, Munich (ISBN 3-446-17198-3).

Uhlig, K. (1999). Discovering Polyurethanes Carl Hanser Verlag, Munich (ISBN 3-446-21022-9).Woods, G. (1990). The ICI Polyurethanes Book, 2nd edn., ICI Polyurethanes and Wiley, Everberg and

Chichester (ISBN 0-471-92658-2).

Documents

MDI and TDI: Safety, Health and the Environment. · 2 Handling MDI and TDI Pride in safety Safety is a critically important aspect of all activities involved in the handling of chemicals